NAVAL FACILITIES ENGINEERING COMMAND
Washington, DC 20374-5065
NFESC
Technical Report
TR-2193-ENV
FINAL
AIR SPARGING GUIDANCE DOCUMENT
Contract N47408-95-D-0730
Delivery Order No. 0090/0123
Prepared for
Naval Facilities Engineering Service Center
1100 23rd Avenue
Port Hueneme, California 93043
Prepared by
Battelle
505 King Avenue
Columbus, OH 43201-2693
August 31, 2001
Approved for public release; distribution is unlimited.
Printed on Recycled Paper
This document has been prepared under the direction of the U.S. Naval Facilities Engineering
Service Center (NFESC). The NFESC is the Navy’s center for specialized facilities
engineering and technology. Products and services include shore, ocean, and waterfront
facilities; environment; amphibious and expeditionary operations; and energy and utilities. As
a member of the Naval Facilities Engineering Command (NAVFAC) team, NFESC provides
worldwide support to Navy engineering activities, fleet and shore activities, the Marine Corps,
and other Department of Defense (DoD) agencies. NFESC provides solutions to problems
through engineering, design, construction, consultation, test and evaluation, technology
implementation, and management support.
The vendors and products, including the equipment, system components, and other materials
identified in this report, are primarily for information purposes only. Although the Navy may
have used some of these vendors and products in the past, mention in this report does not
constitute the Navy’s recommendation for using these vendors or products.
ii
CONTENTS
Figures .......................................................................................................................................................... v
Tables............................................................................................................................................................ v
Acknowledgments........................................................................................................................................ vi
Acronyms and Abbreviations ..................................................................................................................... vii
1.0 Introduction........................................................................................................................................... ix
1.1 Background...................................................................................................................................... 9
1.2 Scope of Document.......................................................................................................................... 2
2.0 Site Characterization and Feasibility Analysis ...................................................................................... 5
2.1 Site Characterization........................................................................................................................ 5
2.2 Air Sparging System Effectiveness ................................................................................................. 5
2.2.1 Contaminant-Related Issues ................................................................................................. 5
2.2.2 Geology- and Hydrogeology-Related Issues........................................................................ 9
2.3 Air Sparging System Implementability.......................................................................................... 11
2.4 Air Sparging System Costs ............................................................................................................ 11
3.0 Regulatory Issues and Permitting ........................................................................................................ 13
3.1 Establishing Cleanup Goals ........................................................................................................... 13
3.2 Performance Objectives ................................................................................................................. 14
3.3 Permitting Issues............................................................................................................................ 15
3.3.1 Well Installation and Boring Permits ................................................................................. 15
3.3.2 Permit to Construct and Operate an Air Pollution Control Device .................................... 15
3.3.3 Certificate of Exemption Permit......................................................................................... 16
3.3.4 Underground Injection Control Permit............................................................................... 17
4.0 System Design and Construction ......................................................................................................... 18
4.1 Target Treatment Area Definition ................................................................................................. 18
4.1.1 Petroleum Hydrocarbons .................................................................................................... 19
4.1.2 Chlorinated Volatile Organic Compounds ......................................................................... 19
4.2 Pilot-Scale Testing......................................................................................................................... 19
4.2.1 Pilot-Scale Testing Equipment ........................................................................................... 20
4.2.2 Pilot-Scale Testing Layout ................................................................................................. 21
4.2.3 Pilot-Scale Test Evaluation ................................................................................................ 21
4.3 Full-Scale Implementation............................................................................................................. 22
4.3.1 Air Injection System........................................................................................................... 23
4.3.1.1 Injection Well Placement ...................................................................................... 23
4.3.1.2 Injection Well Design ........................................................................................... 24
4.3.1.3 Air Compressor Selection ..................................................................................... 27
4.3.2 Vapor Extraction and Treatment System............................................................................ 28
4.3.3 Monitoring Network........................................................................................................... 29
4.3.3.1 Groundwater Monitoring Wells ............................................................................ 29
4.3.3.2 Multilevel Monitoring Points................................................................................ 29
5.0 System Operation, Monitoring, and Optimization............................................................................... 33
5.1 System Startup ............................................................................................................................... 33
5.2 System Operation........................................................................................................................... 34
iii
5.3 System Performance Monitoring ................................................................................................... 34
5.3.1 Operation Parameters ......................................................................................................... 35
5.3.2 Estimating Contaminant Removal...................................................................................... 35
5.3.3 Compliance Monitoring...................................................................................................... 36
5.3.3.1 Groundwater Monitoring ...................................................................................... 36
5.3.3.2 Soil Vapor Monitoring.......................................................................................... 37
5.4 System Optimization...................................................................................................................... 37
5.4.1 Evaluation of Cleanup Goals and Performance Objectives................................................ 37
5.4.2 Optimizing Airflow ............................................................................................................ 39
5.4.3 Optimizing Well Placements.............................................................................................. 39
6.0 System Shutdown, Long-Term Monitoring, and Site Closure............................................................. 41
6.1 System Shutdown .......................................................................................................................... 41
6.2 Long-Term Monitoring.................................................................................................................. 41
6.3 Site Closure.................................................................................................................................... 42
7.0 References............................................................................................................................................ 43
Appendix A:
Appendix B:
Appendix C:
Appendix D:
Appendix E:
Appendix F:
Appendix G:
Appendix H:
Appendix I:
Focused Literature Review ................................................................................................ A-1
Compendium of Competing Remedial Technologies ........................................................ B-1
Properties of Selected VOCs.............................................................................................. C-1
Soil Properties .................................................................................................................... D-1
Air Sparging Economics and Cost Estimating Worksheet................................................. E-1
Overview of Applicable Federal Environmental Regulations ............................................F-1
Air Sparging Pilot-Scale Testing Activity Matrix.............................................................. G-1
Troubleshooting Operational Matrix.................................................................................. H-1
Air Sparging Project Statement of Work Guidance .............................................................I-1
iv
FIGURES
Figure 1-1.
Figure 1-2.
Figure 2-1.
Figure 2-2.
Figure 2-3.
Figure 3-1.
Figure 4-1.
Figure 4-2.
Figure 4-3.
Figure 4-4.
Figure 4-5.
Figure 4-6.
Figure 4-7.
Figure 4-8.
Figure 5-1.
Figure 5-2.
Figure 5-3.
Air Sparging Conceptual Diagram .......................................................................................... 9
Air Sparging Project Flowchart ............................................................................................... 3
Conceptual Site Model ............................................................................................................ 6
Air Sparging Applicability Analysis........................................................................................ 8
Effect Of Heterogeneity On Injected Air Distribution .......................................................... 10
True And Projected Vapor Treatment Costs Over Time At An Air Sparging/SVE Site....... 16
Components Of A Typical Air Sparging System .................................................................. 21
Sample Pilot Test Layout....................................................................................................... 22
Helium Tracer Test Results With Optimal And Suboptimal Site Geology ........................... 23
Standard Design Approach To Injection Well Placement ..................................................... 24
Typical Sparge Well Construction......................................................................................... 25
Air Compressor Performance Curve...................................................................................... 28
Typical SVE Well Construction ............................................................................................ 30
Typical Soil-Vapor/Groundwater Monitoring Point Construction ........................................ 31
Remedial Optimization For Air Sparging Systems ............................................................... 38
Typical Behavior Of An Air Sparging System...................................................................... 39
Optimized Well Placement In High Concentration Areas..................................................... 40
TABLES
Table 1-1.
Table 2-1.
Table 2-2.
Table 3-1.
Table 4-1.
Table 4-2.
Table 5-1.
Where to Locate Answers to Common Questions on Air Sparging ........................................ 2
Site Characterization Parameters for Assessing Feasibility of Air Sparging........................... 7
Example Cases with Contaminants Amenable to Remediation Using Air Sparging............... 9
Example Percent Contaminant Reductions after Air Sparging Application at Selected Sites14
Summary of Pilot Test Activities........................................................................................... 20
Critical Design Considerations for Air Sparging Installations .............................................. 24
Air Sparging System Startup Checklist ................................................................................. 33
v
ACRONYMS AND ABBREVIATIONS
ASTM
American Society for Testing and Materials
bgs
BTEX
below ground surface
benzene, toluene, ethylbenzene, and total xylenes
CA
CAA
CERCLA
cfm
COC
CWA
corrective action
Clean Air Act
Comprehensive Environmental Response, Compensation, and Liability Act
cubic feet per minute
contaminant of concern
Clean Water Act
DCA
DCE
DNAPL
DO
DoD
dichloroethane
dichloroethene
dense, nonaqueous-phase liquid
dissolved oxygen
United States Department of Defense
EIS
EPCRA
ESA
Environmental Impact Statement
Emergency Planning and Community Right-to-Know Act
Endangered Species Act
FIFRA
Federal Insecticide, Fungicide, and Rodenticide Act
GAC
GIS
granular activated carbon
Geographic Information System
HASP
health and safety plan
ID
IDW
inner diameter
investigation-derived waste
LNAPL
light, nonaqueous-phase liquid
MACT
MC
MCL
MCLG
MTBE
MW
Maximum Achievable Control Technology
methylene chloride
maximum contaminant level
maximum contaminant level goal
methyl tert-butyl ether
molecular weight
NAAQS
NAPL
NAVFAC
NCP
ND
NEPA
National Ambient Air Quality Standards
nonaqueous-phase liquid
Naval Facilities Engineering Command
National Oil and Hazardous Substances Pollution Contingency Plan
not detected
National Environmental Policy Act
vii
NFESC
NHPA
NPL
Naval Facilities Engineering Service Center
National Historic Preservation Act
National Priorities List
O&M
OD
OSHA
operations and maintenance
outer diameter
Occupational Safety and Health Administration
PCE
POTW
ppb
ppm(v)
psi(g)
PVC
tetrachloroethylene
publicly owned treatment works
parts per billion
parts per million (by volume)
pounds per square inch (gage)
polyvinyl chloride
QA
QAPP
QA/QC
quality assurance
Quality Assurance Project Plan
Quality Assurance/Quality Control
RAO
RBCA
RCRA
ROD
RPM
remedial action objective
risk-based corrective action
Resource Conservation and Recovery Act
Record of Decision
Remedial Project Manager
SARA
SDWA
SF6
SIP
SOW
SVE
SVOC
Superfund Amendments and Reauthorization Act
Safe Drinking Water Act
sulfur hexafluoride
State Implementation Plan
Statement of Work
soil vapor extraction
semivolatile organic compound
TCA
TCE
TPH
TSCA
trichloroethane
trichloroethene
total petroleum hydrocarbons
Toxic Substances Control Act
USACE
U.S. EPA
UST
United States Army Corps of Engineers
United States Environmental Protection Agency
underground storage tank
VC
VOC
vinyl chloride
volatile organic compound
WBS
Work Breakdown Structure
viii
1.0 INTRODUCTION
This document was developed by the Naval Facilities Engineering Service Center (NFESC) to provide
guidance on selection, design, installation, operation,
optimization and shutdown of air sparging systems. This
guidance document is intended for use by Navy, Marine
Corps, and other Department of Defense (DoD)
Remedial Project Managers (RPMs) and their
contractors. The manual applies the results from fullscale systems, field studies, and research to provide a
concise yet complete life-cycle approach to air sparging
design and implementation.
and/or removed via soil vapor extraction (SVE) in the
vadose zone. For semivolatile contaminants, such as
diesel and jet fuels, air stripping is not the removal
mechanism. Rather, the primary removal mechanism is
stimulated microbial activity caused by the introduction
of dissolved oxygen, which increases the biodegradation
rate of the contaminant in the saturated zone. The major
components of a typical air sparging system, shown in
Figure 1-1, include an air sparge/injection well, a compressor or blower to supply air, monitoring points and
wells, and an optional SVE system.
For sites contaminated with halogenated and nonhalogenated volatile organic compounds (VOCs) as a
result of leaking underground storage tanks, pipelines, or
other accidental releases, air sparging is a viable remedial option. The use of air sparging to remove VOCs has
been demonstrated successfully; in fact, in many cases,
air sparging is the most cost-effective remedial alternative. As with any in situ technology, well-engineered
design followed by proper installation and operation are
essential for achieving remedial goals and site closure.
1.1 Background
Air sparging is an innovative in situ treatment technology that uses injected air to remove volatile or biodegradable contaminants from the saturated zone. The
primary application of air sparging entails the injection
of air directly into the saturated subsurface to remove
volatile contaminants such as solvents and gasoline
from the dissolved phase to the vapor phase through air
stripping. The stripped compounds are then biodegraded
FIGURE 1-1.
Air Sparging Conceptual Diagram
ix
design and construction, operation and maintenance,
and site closure. The need for a life-cycle approach to
system design, optimization, and long-term monitoring
is also addressed. In general, this document attempts to
answer the most common questions an RPM might have
with respect to air sparging. Table 1-1 provides a quick
reference to finding answers to these questions within
the document. Figure 1-2 is a flowchart showing the
general approach to implementing air sparging at a site.
1.2 Scope of Document
The primary goal of this document is to provide
RPMs and others with a management resource for the
selection and cost-effective implementation of air sparging groundwater remediation systems. As such, the
document provides detailed information covering all
aspects of air sparging including feasibility analysis,
regulatory and permitting issues, pilot testing, system
TABLE 1-1. Where to Locate Answers to Common Questions on Air Sparging
Question
1. Will air sparging work at my
site?
Answer Location
Section 2.0. Site Characterization and Feasibility Analysis: Provides
information regarding site characterization requirements as well as the effect
of site-specific data, such as contaminant type and geology, on air sparging
effectiveness, implementability, and cost.
Appendix C. Properties of Selected VOCs: Provides physical properties
of VOCs necessary in evaluating air sparging feasibility.
2. How much will it cost?
3. Where can I find more information on the field application of
air sparging at other sites?
4. Is air sparging the best
technology for my site?
5. What regulatory and permitting
issues do I need to consider
when using air sparging?
6. How are air sparging systems
designed?
7. Does air sparging require
predesign (pilot) studies?
8. How long will it take to achieve
cleanup goals?
9. How do I know if the system is
operating effectively and
efficiently?
10. When can I stop operating the
system?
11. The system is not operating/
performing as intended.
What’s wrong?
12. What are the key issues for my
contractor to focus on?
Appendix D. Soil Properties: Provides soil properties to aid in evaluating
air sparging feasibility.
Appendix E. Air Sparging Economics and Cost Estimating Worksheet:
Summarizes air sparging economics and provides a worksheet to quickly
estimate budgetary costs.
Appendix A. Focused Literature Review: Provides the results and
lessons learned from other air sparging field applications.
Appendix B. Compendium of Competing Remedial Technologies:
Evaluates competing remedial technologies to air sparging.
Section 3.0. Regulatory Issues and Permitting: Identifies potentially
applicable federal, state, and local regulations and permitting requirements.
Appendix F. Overview of Applicable Federal Environmental
Regulations: Summarizes federal regulations that may be applicable at air
sparging sites.
Section 4.0. System Design and Construction: Describes pilot-scale
testing requirements and full-scale design and construction considerations.
Appendix G. Air Sparging Pilot-Scale Testing Activity Matrix:
Summarizes pilot-scale testing activities and interpretation of pilot study
data.
Section 5.0. System Operation, Monitoring, and Optimization:
Provides information on how to ensure that the air sparging system is
operating in a cost-effective manner and how to evaluate progress toward
achieving cleanup goals.
Section 6.0 System Shutdown, Long-Term Monitoring, and Site
Closure: Describes when and how to stop system operation and methods
to obtain site closure.
Appendix H. Troubleshooting Operation Matrix: Provides a list of
common problems encountered during air sparging operation and a
recommended solution.
Appendix I. Air Sparging Statement of Work Guidance: Provides
guidance for preparation of a statement of work for an air sparging site.
2
FIGURE 1-2.
Air Sparging Project Flowchart
3
In addition, the following appendices are designed to
expand on the main text and guide the RPM in other
aspects of air sparging project management:
Appendix E: Air Sparging Economics and Cost
Estimating Worksheet
Appendix F: Overview of Applicable Federal
Environmental Regulations
Appendix G: Air Sparging Pilot-Scale Testing
Activity Matrix
Appendix H: Troubleshooting Operation Matrix
Appendix I: Air Sparging Project Statement of
Work Guidance
Appendix A: Focused Literature Review
Appendix B: Compendium of Competing Remedial
Technologies
Appendix C: Properties of Selected VOCs
Appendix D: Soil Properties
4
2.0 SITE CHARACTERIZATION AND FEASIBILITY ANALYSIS
Air sparging is a relatively simple and effective
treatment technology that has a proven record of successful performance when properly applied. This section
is designed to aid RPMs in determining if air sparging
will achieve objectives at a given site based on the
results of site characterization and technical considerations such as contaminant type, geology, hydrogeology,
and other factors. Technical feasibility issues are addressed by considering effectiveness, implementability,
and costs of air sparging systems.
A feasibility analysis is a necessary first step in
determining if air sparging will be the best technology
for remediation at a site, and typically is accomplished
as part of a Feasibility Study or Corrective Action Plan.
In order to make an informed decision as to whether or
not air sparging is the most appropriate remedy, it also
is necessary to evaluate other competing treatment technologies. Although technology evaluation is not the focus
of this document, a compendium of competing technologies with their advantages and limitations respective to
air sparging is provided in Appendix B, and serves as a
starting point for evaluation.
purposes. The following issues are common reasons for
failure of site investigation programs:
q Inadequate preparation and planning can cause
cost overruns and incomplete site characterization.
q Inexact definition of geology/hydrogeology can
cause the selection of an inefficient remediation
method.
q Poor definition of contaminant distribution leads
to incomplete site remediation.
q Inadequate collection of chemical data can cause
the selection of an inappropriate remediation
method.
To avoid the difficulties listed above, Table 2-1
identifies the site characterization parameters needed for
the feasibility analysis of an air sparging site.
2.2 Air Sparging System Effectiveness
Effectiveness is a measure of the remediation technology’s ability to meet remedial objectives based on
site-specific conditions. The potential effectiveness of
air sparging at a site must be carefully evaluated during
the feasibility analysis. Figure 2-2 is a flowchart that
serves as an initial screening methodology for determining if air sparging is appropriate for a given site.
The following sections summarize contaminant,
geology, and hydrogeology-related issues that impact
the effectiveness of air sparging.
2.1 Site Characterization
Site conditions and contaminant characteristics, as
defined by the conceptual site model, drive decisions
determining whether or not air sparging is the most
appropriate and effective technology for a site. Current
and site-specific data are necessary for the feasibility
analysis and, if a good conceptual site model has not
been developed, additional data will need to be collected. Figure 2-1 shows the elements of a good conceptual site model.
A conceptual site model (CSM) is a useful engineering management tool that summarizes all available
site history, site characterization, receptor survey, and
land use data into a form that helps decision makers. For
existing data, the project manager must determine
whether the data set was collected properly and if it is
current enough to be useful. For example, if the most
recent assessment of contaminant concentrations is
more than five years old, additional, more recent contaminant data are likely to be needed prior to remedy
selection. The existing data set should be reviewed to
ensure that it is sufficient for site screening and design
2.2.1
Contaminant-Related Issues
q Air sparging is typically effective at removing
dissolved VOCs, and has potential application for
low levels of light, nonaqueous-phase liquid
(LNAPL), or dense, nonaqueous-phase liquid
(DNAPL). If recoverable free product is present
at a site, it should be removed to the extent
practicable and the site should then be evaluated
for groundwater remediation requirements.
LNAPL free-product recovery can be evaluated by
methods described in Hoeppel and Place (1998).
5
FIGURE 2-1.
Conceptual Site Model
6
TABLE 2-1. Site Characterization Parameters for Assessing Feasibility of Air Sparging
Objective
Site history
Site geology/
hydrogeology
Contaminant
type and
distribution
Geochemical
assessment
Receptor
assessment
Political
assessment
Parameter
Site engineering plans
Chemical inventory records
Contaminant release records
Subsurface geology
Soil type/stratification
Groundwater depth
Groundwater velocity
Groundwater direction
Hydraulic gradient
Contaminant type
Contaminant(s) of concern
LNAPL thickness (if present)
LNAPL recovery potential
(if present)
Volume of contaminant
released
Dissolved oxygen
Redox potential
pH
Conductivity
Nitrate
Fe(II)
Methane
Identify potential receptors of
groundwater contamination
Identify potential receptors of
vapor migration
Identify regulatory authorities
and define the remedial
action objective (RAO).
Comments
The primary purpose of this assessment is to determine which
parameters have already been characterized and which must
still be collected.
Collect data within the target treatment area. This can involve
collecting soil cores, installing groundwater wells, performing
aquifer characterization tests, and monitoring groundwater
elevations. It is useful to take water-level measurements at
several times during the year and over several years so
seasonal and long-term variations in groundwater flow velocity
and direction can be evaluated.
It is necessary to collect data that is sufficient to define the
extent of the contaminant plume both horizontally and vertically,
as well as to understand plume movement over time.
Contaminant distribution data should be plotted on isocontour
maps and on cross-section profiles to visualize the lateral and
vertical extent of the plumes.
Define horizontal and vertical distribution through multilevel
wells for thicker contaminant plumes; Define horizontal
distribution for thinner contaminant plumes. These parameters
are optional for most air sparging sites, but critical when the
application is meant to enhance bioremediation.
Conduct a site visit and examine site boundaries. Identify
persons or resources that could be impacted by the
contamination and remediation process.
Early contact with the appropriate regulatory agencies is
encouraged, as regulatory guidelines may exist that must be
followed during site characterization.
q Table 2-2 lists contaminants that have been successfully removed via air sparging. In general, for
air sparging to be effective, contaminants must be
either sufficiently volatile to strip out of the
groundwater, or aerobically biodegradable. Additional testing is required to evaluate sites with
compounds for which there are no data supporting
contaminant removal via air sparging.
aqueous solubility (see Table C-1). For example,
tetrachloroethylene (PCE) has a relatively high
Henry’s law constant (1.8 × 10-2 atm-m3/mol) due
to both its high volatility and low aqueous
solubility. Even though acetone has a relatively
high vapor pressure (180 mm Hg), it has a low
Henry’s constant (3.88 × 10-5 atm-m3/mol) due to
its high water solubility (1,000,000 mg/L). In
general, compounds like acetone and MTBE, with
relatively low Henry’s constants will be more
costly to treat with air sparging because a greater
flowrate of injected air and/or extended treatment
duration are likely to be required to achieve
remedial objectives.
q In many geological settings, groundwater contaminated with petroleum hydrocarbons and/or
dissolved chlorinated solvents can be readily
remediated through air sparging. These compounds generally exhibit good strippability as
characterized by a high Henry’s law constant.
The Henry’s law constant can be approximated by
the ratio of a compound’s vapor pressure to its
7
8
FIGURE 2-2.
Air Sparging Applicability Analysis
TABLE 2-2. Example Cases with Contaminants Amenable to Remediation Using Air Sparging
Compound(s)
Initial Maximum
(a)
Concentration
811 mg/L
11 mg/L
11,701 mg/L
11,510 mg/L
38.1 mg/L
470; 14; 0.052; 91; 0.93; 36; 69;
17; 3.6; 11 (all mg/L)
2.0 mg/L; 7,010 mg/L
22,000 mg/L; 9,300 mg/kg (soil)
41,000 mg/L; 150,000 mg/L
(b)
5.9 g
20-50 mg/L
489 mg/L
6,670; 9,870; 26,400 (all mg/L)
1.0 mg/L
94 mg/L; 960 mg/L; 3,000 mg/L
>10,000 mg/kg (soil)
Reference
Benzene
Covell and Thomas, 1997
BTEX
Hartley et al., 1999
BTEX
Klemm et al., 1997
BTEX
Muehlberger et al., 1997
BTEX
Klemm et al., 1997
BTEX; 1,1-DCA; 1,2-DCA; cis-DCE;
Maheux and McKee, 1997
trans-DCE; MC; PCE; 1,1,1-TCA; TCE; VC
BTEX; MTBE
Damera et al., 1997
BTEX; TPH
Strzempka et al., 1997
Ethylbenzene; xylenes
Kraus et al., 1997
MTBE
Bruce et al., 1998
PCE
Marnette et al., 1999
PCE
Dreiling, 1998
PCE; TCE; cis-DCE
Hughes and Dacyk, 1998
TCE
Aubertin and Hise, 1998
TCE; DCE; VC
Kershner and Theoret, 1997
TPH
Basinet and Wollenberg, 1997
(a) Concentration in groundwater unless noted.
(b) Laboratory study in which 5.9 g of MTBE was injected into large-scale reactor.
BTEX = benzene, toluene, ethylbenzene, and total xylenes.
TCA = trichloroethane.
DCA = dichloroethane.
TCE = trichloroethene.
DCE = dichloroethene.
TPH = total petroleum hydrocarbons.
MC
= methylene chloride.
VC = vinyl chloride.
MTBE = methyl-tert-butyl ether.
q At most air sparging sites, the volatilization process is the primary mechanism for mass recovery
and can account for up to 99% of the mass
removed (based on typical biodegradation rates of
8 kg/day vs. 810 kg/day for volatilization rates in
Leeson et al., 2001). However, sites contaminated
with SVOCs, such as diesel and jet fuels that cannot be removed effectively via volatilization, may
be remediated through enhanced aerobic biodegradation. If the goal of the air sparging system is to
enhance bioremediation by increasing groundwater dissolved oxygen (DO) concentrations, and
the site already has DO concentrations greater than
2 mg/L, then air sparging may not be warranted.
2.2.2
q Site geological conditions such as stratification,
heterogeneity, and anisotropy will prevent uniform
airflow through the medium, thus reducing air
sparging effectiveness. For in situ air sparging
applications, good characterization of the geology
in the area where the air sparging system is to be
installed is critical. The subsurface geology
should be evaluated by collecting at least one
continuous soil core from ground surface to the
bottom of the contaminated aquifer in the area
where air sparging is being considered. A hydrogeologist should evaluate the soil core to determine the soil type and to identify the depth and
location of distinct soil layers that may influence
airflow.
Geology- and HydrogeologyRelated Issues
q Figure 2-3 depicts the potential effect of geologic
conditions on injected air distribution. If the subsurface is relatively homogenous, the airflow distribution pattern will tend to form a symmetrical,
conical shape. If thick, continuous confining
q Air sparging is best suited to sites with sandy soils
and medium to shallow aquifer depths at less than
50 ft below ground surface (bgs).
9
Petroleum Hydrocarbon
Release
Air Injection
Residual
Contaminants
Vadose Zone
Water Table
Smear Zone
Dissolved Phase
Contamination
Saturated Zone
Air Channels
Confining Layer
Petroleum Hydrocarbon
Release
Air Injection
Residual Contaminants
Vadose Zone
Water Table
Dissolved Phase
Contamination
Smear Zone
Saturated Zone
Air Channels
Confining
Lenses
Confining Layer
02-3.PPT
FIGURE 2-3.
Effect of Heterogeneity on Injected Air Distribution
layers are present in the contaminated zone, they
may prevent airflow from reaching the contaminants altogether. If thin, discontinuous layers are
present, there will be less disruption to airflow,
but preferential flowpaths may develop. Air flowpaths that are formed during air sparging are
sensitive to small changes in soil permeability, so
identification of layers of lower permeability
material between the water table and greatest
depth of contaminant penetration is important.
not the best remedial approach. In general, sites
having high clay or silt content in soils with
hydraulic conductivities less than 1 × 10-3 cm/s are
not typical candidates for this technology.
However, a recent pilot test has demonstrated
successful contaminant removal using pulsed air
sparging in a low permeability, highly stratified
formation with hydraulic conductivities on the
order of 6 × 10-7 to 3 × 10-4 cm/s (Kirtland and
Aelion, 2000). In these suboptimal cases, pilot
testing may still be warranted. Appendix D lists
typical hydraulic conductivity values for a variety
of soil types.
q Although stratification and heterogeneity may
reduce effectiveness, their presence does not
directly lead to the conclusion that air sparging is
10
q At sites with LNAPL present, the majority of the
contaminant mass is often contained in the smear
zone or a band of residual product just above and
below seasonal water table levels. If a smear zone
is present, air sparging may be an effective
approach because air moves vertically upward
through this region. SVE alone would not be able
to fully address the residual LNAPL source in the
smear zone due to the seasonal submergence of
this zone by the fluctuating water table.
q If SVE is not necessary, minimal operational oversight is required once the system is installed and
no wastestreams are generated that require treatment. If SVE is required, soil vapor treatment
prior to discharge to the atmosphere is likely to be
required. This will necessitate obtaining an air
discharge permit and additional manpower to
operate and maintain the treatment equipment.
Limitations
q Because air sparging increases the rate of contaminant volatilization, it is important to be aware of
the potential for migration of VOC-impacted
vapor to human and/or ecological receptors at
potential levels of concern. An SVE system can
be used to reduce or eliminate vapor migration
problems, but the proximity of the site to buildings
or other structures should be taken into careful
consideration. SVE is widely used and is one of
the U.S. EPA’s presumptive remedies for the
remediation of VOC-contaminated vadose zone
soils. SVE is relatively easy to implement, but
depth to groundwater should generally be greater
than 5 ft bgs to prevent SVE well submergence.
2.3 Air Sparging System Implementability
Implementability is a measure of both the technical
and administrative feasibility of the chosen remediation
technology. Implementability issues relating to air sparging systems include the following advantages and limitations:
Advantages
q Application of the technology is widely recognized
by the regulatory community as an effective remedial technology for removing volatile contaminants
from groundwater.
q If air sparging is applied to contain a dissolved
phase plume, at a high air injection rate in a
sparging barrier configuration, the injection of air
into the subsurface can produce a zone of reduced
hydraulic conductivity. If operation of the air
sparging system is not managed properly, this
could divert the plume away from the zone of air
sparging influence and reduce treatment
efficiency. Proper management includes pulsing
air flow which allows water to flow through the
sparged zone when the system is turned off.
q Implementation is relatively simple, because only
readily available commercial equipment is utilized
(i.e., polyvinyl chloride [PVC] well casing,
compressors or blowers, etc.). The equipment is
relatively easy to install and causes minimal
disturbance to site operations.
q Cleanup times are relatively short, typically taking
less than two years to achieve performance
objectives.
q Use of low-cost, direct-push well installation
techniques is possible. Direct-push technologies
are most applicable in unconsolidated sediments
and at depths of less than 30 ft. (Although, in
relatively coarse-grained lithologies, direct-push
rigs may experience some difficulty in obtaining
good material recovery and specialized equipment
may be needed to obtain relatively undisturbed
samples from depths greater than 10 ft [Kram,
2001]). In soils where utilizing this technology is
feasible, this option offers the advantage of being
more rapid and less expensive than traditional
drilling techniques such as the hollow-stem auger
method.
2.4 Air Sparging System Costs
The potential economic benefit of air sparging has
been an important driving force for utilization of this
technology. The main categories of costs for air sparging projects are initial investment and operations and
maintenance (O&M). Initial investment costs include
expenditures such as additional site characterization,
pilot-scale testing, design, and system construction,
whereas O&M costs can include monitoring, vapor treatment, and site decommissioning costs. Although system
design and installation costs may be comparable to other
competing technologies, O&M costs may be significant11
ly reduced due to the typically short duration of operation. Developing a life-cycle approach to system design
and optimization can help to minimize equipment and
O&M costs. Typically, full-scale air sparging remediation costs range from $150,000 to $350,000 per acre of
groundwater treated (FRTR, 2001). The remaining sections of this document will highlight ways to improve
system design and operation to ensure cost-effective
implementation throughout the life of the project. Air
sparging project costs are discussed in more detail and
an initial cost-estimating worksheet is provided in
Appendix E.
The following is a list of the major factors that
impact project design and installation and O&M costs:
wells required to adequately cover the target treatment
area. The required number of wells is controlled by the
areal extent of the contamination and the subsurface air
distribution characteristics. The costs for well installation and construction will also increase as the depth to
the contaminated zone increases and the drilling
becomes more costly. Capital equipment costs are
impacted by the air injection and extraction flowrates,
which relate to compressor and blower sizing, and by
vapor treatment requirements, which determine the type
and capacity of air pollution control equipment selected.
The O&M costs are influenced primarily by those
factors that tend to increase the time required to reach
remedial action objectives. The presence of nonaqueousphase liquids (NAPLs) can significantly increase project
duration because they provide a continuing source of
groundwater contamination. Site subsurface characteristics are also important because the achievable air
injection rate and/or extraction rate affects the rate of
contaminant removal and therefore the project duration.
The soil characteristics also impact the required operating pressure for injection and the required vacuum for
extraction, which can increase energy use at the site. As
discussed in Section 3.0, vapor treatment requirements
are often the most significant O&M costs for an air
sparging project coupled with SVE. The replacement
and disposal of activated carbon or the need for supplemental fuel for thermal/catalytic oxidation plays a large
role in project economics.
q
q
q
q
q
q
q
q
q
Type of contaminant
Area and depth of contaminant
Depth of groundwater
Site geology
Air sparging/SVE well spacing
Drilling method
Required flowrate and vacuum and pressure
Treatment duration
Regulatory requirements (e.g., monitoring,
permitting, etc.)
q Vapor treatment requirements.
The installation costs of an air sparging system are
based primarily on the number of air sparging and SVE
12
3.0 REGULATORY ISSUES AND PERMITTING
Numerous environmental regulations will impact
the design, installation, and operation of an air sparging
system. This section summarizes regulatory and permitting issues that must be considered for remediation projects using air sparging technologies. In the planning
phase, it is important to research the regulatory framework involved because important issues such as limits
on VOC emissions and stringent cleanup standards can
significantly impact feasibility. Numerous federal regulations and executive orders may impact a remediation
project (Appendix F provides a summary of these regulations), including:
However, state and local regulations typically are
the most critical because establishing site cleanup goals,
permitting, and site closure negotiations take place under
state and local jurisdictions. The majority of the regulatory compliance work will include obtaining permits
from, and submitting reports to, state or local agencies.
Although a detailed review of state and/or local regulations is beyond the scope of this guidance document,
the following general considerations for establishing
cleanup goals, performance objectives, and permitting
requirements will apply to most sites.
3.1 Establishing Cleanup Goals
q Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA)
Remediation projects typically will fall under the
jurisdiction of CERCLA, RCRA, or state and local
underground storage tank (UST) programs. In most cases,
the cleanup goals will consist of either site-specific riskbased levels or regulated concentrations, such as maximum contaminant levels (MCLs), established for contaminants in groundwater. The risk-based remediation
goals usually are calculated based on industrial and/or
residential exposure scenarios and derived using standard contaminant partitioning and transport equations.
These risk-based approaches are presented in the American Society for Testing and Materials (ASTM) Standard
Guide for Risk-Based Corrective Action (RBCA) at
petroleum release sites (ASTM, 1996). Most states
either have their own risk-based guidance for low-risk
site closure or accept a RBCA-type approach. Progress
towards remedial goals should be tracked and reviewed
on a quarterly basis or as new compliance and system
monitoring data become available. The following suggestions should be considered when establishing or
reviewing cleanup objectives for an air sparging remediation project:
q Superfund Amendments and Reauthorization Act
(SARA)
q Emergency Planning and Community Right-toKnow Act (EPCRA)
q Resource Conservation and Recovery Act (RCRA)
q Clean Water Act (CWA)
q Safe Drinking Water Act (SDWA)
q Clean Air Act (CAA)
q Occupational Safety and Health Administration
(OSHA) rules
q Endangered Species Act (ESA)
q Executive Order No. 11988, Floodplain
Management
q Executive Order No. 11990, Protection of
Wetlands
q Identify opportunities for modifying cleanup goals
based on regulatory changes or updated contaminant toxicity information. Often stringent cleanup
levels such as MCLs may be required initially, but
through a site-specific risk assessment and negotiation with state/local regulators, more appropriate and/or feasible cleanup levels may be agreed
upon.
q Federal Insecticide, Fungicide, and Rodenticide
Act (FIFRA)
q National Environmental Policy Act (NEPA)
q National Historic Preservation Act (NHPA)
q Toxic Substances Control Act (TSCA).
13
q Utilize groundwater monitoring data or develop
site-specific groundwater transport models to help
negotiate cleanup levels or to demonstrate that
levels of residual contamination at the site do not
pose a threat to potential receptors.
sparging systems achieve greater than 90% reduction in
contaminant concentrations (Bass et al., 2000). However, permanent reductions in groundwater VOC concentrations greater than 90% can be insufficient to meet
stringent cleanup standards. Table 3-1 shows that sites
with similar percent reductions in total contaminant mass
can have varying success towards achieving cleanup
objectives. With a 92% reduction in TCE groundwater
concentrations, the United States Army Corps of Engineers (USACE) could not meet the stringent cleanup
standard of 5 mg/L (USACE, 1998). Alternately, a
greater than 99% reduction of TCE concentrations in
groundwater was reported by Glass (2000), which effectively met the 1,000-mg/L remedial objective.
As with any remediation technology, air sparging
should be utilized when its operation is cost-effective.
At sites where the air sparging system reaches asymptotic levels of VOC recovery and system operation loses
its cost-effectiveness, a transition to other remedies
(such as monitored natural attenuation) should be considered (see Section 6.0). To avoid regulatory bottlenecks, the performance objectives and the site closeout
strategy should be discussed with regulatory authorities
during system design and documented in the site’s
remediation work plan or Record of Decision (ROD) as
appropriate. Some performance objectives or issues to
consider include:
q Identify sites where engineering and institutional
controls can be used to reduce receptor exposure
to contaminated soil or groundwater. For example, the cleanup requirements can be reduced with
the use of appropriate deed restrictions which
establish the site as a Brownfield, limit future land
use, and prevent future residential development.
These options must be discussed with legal counsel and the long-term use of the site should be
considered. Land use controls may not always be
feasible for federally owned sites.
q Where the contaminants of concern are petroleum
hydrocarbons, attempt to remove remediation
projects from RCRA or CERCLA authority and
place them under state and local UST programs.
This change results in fewer regulatory requirements and increased options for site-specific, riskbased cleanup.
3.2 Performance Objectives
q Establish contaminant mass removal objectives
rather than agreeing to meet stringent groundwater
contaminant concentrations. For example, data
from other full-scale air sparging systems indicate
The development of performance objectives for air
sparging systems is critical to cost-effective remediation
because air sparging alone may not achieve cleanup
goals. Air sparging is effective at removing contaminant
mass. Surveyed literature indicates that over half of air
TABLE 3-1. Example Percent Contaminant Reductions after Air Sparging Application
at Selected Sites
Compound(s)
DCE, PCE, TCE, VC
Remedial Action
Objective
TCE < 5 mg/L
VC < 1 mg/L
DCE, PCE, TCE
PCE < 5 mg/L
TCE < 5 mg/L
DCA, DCE, TCE, VC
TCE <1,000 mg/L
Percent Reduction
for Each Contaminant
DCE 100%
TCE 92%
VC 100%
DCE 9%
PCE 82%
TCE 95%
TCE 99.9%
Duration of
Operation
12 months
Reference
USACE, 1998
9 months
Hughes and Dacyk, 1998
8 months
Glass, 2000
BTEX 99.9%
15 months Hartley et al., 1999
BTEX < 2 mg/L
E
98%
10 months Kraus et al., 1997
E < 680 mg/L
(a)
X
99%
X < 1,750 mg/L
(a) Remedial action objectives not provided for this site, so MCLs were added for comparison.
BTEX
Ethylbenzene and Xylenes
14
will require well or boring permits. Applications for
these permits usually request a description of the well
construction details along with information regarding
subsurface lithology. Right-of-way permits also may
have to be obtained for the installation of monitoring
wells off-site, near roadways, or on public property.
that the majority of systems achieve significant
reductions in contaminant mass; therefore, 80%
mass removal can be proposed as a performance
objective.
q Establish criteria to trigger a transition to monitored natural attenuation once VOC recovery by
the air sparging/SVE system has reached asymptotic levels and VOC levels in groundwater have
been reduced compared to initial baseline levels.
3.3.2
Additionally, before the air sparging/SVE system is
installed, both a permit to construct and a permit to
operate an air pollution control device typically will be
required. These permits can involve separate applications or a combined single application and usually are
submitted to local Air Pollution Control Boards or Districts at the county level. The application for these permits typically include the following elements:
q The SVE component of air sparging typically is
the most costly aspect of system operation.
Consider establishing performance goals for usage
of the SVE system. Determine the contaminant
loading where biological degradation in the vadose
zone is sufficient to control contaminated vapor
migration/releases and discontinue SVE operation
at this point. (Discontinuing SVE operations may
require increased vapor monitoring requirements
to ensure safety and regulatory compliance.)
q Site location diagrams and system piping and
instrumentation diagrams
q Contaminant rebound following system shutdown
is an important consideration in measuring air
sparging performance. Consider leaving the air
sparging system on standby (off, but still functional) for a 12- to 18-month period after turning
off the system. If significant rebound occurs,
reinitiate operation. This contingency will help
ease regulatory concerns regarding discontinuation
of system operation prior to achieving cleanup
goals and yield substantial savings in mobilization
and startup costs if reinitiation is required.
q List of major pieces of equipment (e.g., blower,
thermal oxidizer)
q List of stack parameters (e.g., height, diameter,
flowrate)
q Description of flow monitoring and inlet/outlet
vapor phase monitoring techniques
q Estimates of criteria air pollutant emissions (e.g.,
NO2, SOX, CO, particulate matter)
q Estimates of hazardous air pollutant emissions
(e.g., benzene).
3.3 Permitting Issues
Permitting is an important aspect of air sparging
regulatory compliance as well as a significant cost consideration. The following sections discuss the permits
typically required for the installation and operation of an
air sparging system including well installation and boring permits, air permits, and underground injection control permits.
3.3.1
Permit to Construct and Operate an
Air Pollution Control Device
Several issues are involved in these permit applications that can impact the performance and economics of
the air sparging remediation project. The selection of the
type of air pollution control equipment has a substantial
impact on project economics. Pilot test data can be used
to select and size the air pollution control device (e.g.,
thermal or catalytic oxidizer or granular activated carbon system), but a practitioner must take into account
the fact that the VOC removal rate will drop dramatically over time from the initial levels. Figure 3-1 illustrates the impact of decreasing mass removal rate on
vapor treatment costs by displaying the following data
versus time:
Well Installation and Boring Permits
Local agencies, such as a county Department of
Health, often require permits for subsurface installations. All sparge wells, SVE wells, soil vapor monitoring points, and groundwater monitoring wells typically
15
FIGURE 3-1.
True and Projected Vapor Treatment Costs Over Time at an Air Sparging/SVE Site
q VOC extraction rate data from an air
sparging/SVE system (green)
optimize the selection of vapor treatment technology
because system operating costs can be more than
doubled if a less than optimal vapor treatment
technology is used.
The permit should contain provisions to change out
air pollution control equipment as the VOC extraction
rates and the resulting vapor treatment required diminishes. Once granted, this permit will set emission limits
and monitoring requirements for each pollution control
device. The permit usually will require weekly or
monthly monitoring and periodic submission of reports
that document the required performance parameters of
the air pollution control device.
q True cost per pound of VOC extracted (yellow)
q Projected cost per pound of VOC extracted for
thermal oxidation (blue)
q Projected cost per pound of VOC extracted for
granular activated carbon (GAC) (red).
During the first three months of the project, thermal
oxidation was the most cost-effective technology because VOC levels were high (5,000 to 500 ppmv) and
significant heat value was present in the extracted soil
vapor. As the VOC levels declined down to levels below
500 ppmv, the need for supplemental fuel continued to
increase, and eventually thermal oxidation costs reached
a level that made GAC purchase and disposal costs
competitive. Figure 3-1 shows that it is important to
3.3.3
Certificate of Exemption Permit
At sites where an air pollution control device is not
required (i.e., SVE is not required), the local air pollution regulatory agency may require a Certificate of
Exemption permit. This permit documents that direct
16
discharge from the air sparging system will not impact
air quality above certain allowable limits.
3.3.4
The remedial project manager should determine if an
underground injection control permit is required at the
site. These permits typically include provisions for the
following:
Underground Injection
Control Permit
q Classification of the injection well(s)
Some states regulate the injection of air into the
subsurface through underground injection control programs. These programs often cover injection wells used
for innovative remediation technologies such as air
sparging, in situ oxidation, and enhanced bioremediation.
q Classification and protection of the affected
groundwater
q Requirements for abandonment, monitoring, and
reporting.
17
4.0 SYSTEM DESIGN AND CONSTRUCTION
In a case study of 49 air sparging sites, Bass et al.
(2000) reported that groundwater VOC concentration
reductions ranged from 27% to almost 100%. The overall success of the systems varied due to differing
designs, construction techniques, and operational conditions, which indicates that correct design and construction of an air sparging system is necessary for successful
implementation. This section discusses the following
aspects of air sparging system design and construction:
q
q
q
q
q
exceed the biodegradation capacity of the vadose
zone and/or impact ambient air quality above the
appropriate regulatory thresholds.
q Air sparging, without SVE, can be designed to
deliver a mixture of oxygen to the saturated zone
to stimulate microbial growth and therefore
enhance aerobic biodegradation of target compounds dissolved in groundwater. This approach
can be an option if the contaminants are
aerobically biodegradable SVOCs.
Target treatment area definition
Pilot-scale testing
Air injection system design
SVE system design
Monitoring network placement and construction.
4.1 Target Treatment Area Definition
The target treatment area is the area where the air
sparging system will be installed to achieve the most
effective treatment. The area will be defined based on
the site characterization data and regulatory requirements.
It may encompass the source zone, the dissolved plume,
localized areas with elevated concentrations within the
plume, or the downgradient boundary of the dissolved
plume. In determining the target treatment area for an
air sparging system, development of a conceptual site
model is necessary as discussed in Section 2.1 of this
manual. The conceptual site model will help determine
the potential feasibility of air sparging, the most effective location for pilot testing and full-scale system
installation, and facilitate understanding among all
involved parties.
Most practitioners advocate targeting the source
zone for remediation of petroleum-contaminated aquifers, while targeting the localized areas with elevated
concentrations within the dissolved plume is recommended for chlorinated solvent-contaminated aquifers.
In general, if the source zone can be located and
remediated, then the remaining dissolved plume will
dissipate rapidly through natural attenuation processes.
Remediation outside the source area is warranted,
however, when further migration of a recalcitrant
chemical (e.g., TCE or MTBE) must be prevented.
Location of the target treatment zone is dependent
on the contamination type, distribution, and the proximity to receptors. Contaminants commonly are classified into general types based on similar sources and
chemical properties. These properties can affect the
optimal density and location of sparging wells, as discussed in Sections 4.1.1 and 4.1.2.
Air sparging relies upon two different mass removal
mechanisms: (1) air stripping, and (2) aerobic biodegradation. The percentage of mass removed by these two
mechanisms can vary widely and can be influenced by
system design. At most air sparging sites, air stripping is
the primary mechanism for VOC removal, and enhanced biodegradation through aquifer oxygenation is
usually of secondary importance. The relative importance of the above mechanisms should be considered
when designing an air sparging system. Air sparging
systems can be designed and implemented in the following ways:
q Air sparging can be used to restore aquifer water
quality at the source, throughout the plume, or as a
barrier to prevent elevated concentrations from
passing by a selected boundary.
q Air sparging, with SVE, can be designed to operate at high injection flowrates (6 to 20 cubic feet
per minute [cfm]) to effectively partition contaminants from the groundwater into the vapor phase.
The volatilized contaminants are then captured in
the vadose zone by the SVE system and treated
before release to the atmosphere.
q Air sparging, without SVE, can be used to partition VOCs from the groundwater into the vapor
phase for aerobic biodegradation in the vadose
zone. In this approach, soil vapor monitoring is
necessary to establish that the system does not
18
4.1.1
Petroleum Hydrocarbons
ing system location may be treatment within localized
areas of elevated concentrations throughout the plume
and/or location of a system at the leading edge of the
plume. If the source zone can be identified, treatment of
the source zone is recommended to shorten the remediation time.
For petroleum hydrocarbon contamination, the target treatment area is influenced by three factors:
q Typically, the more hazardous components (i.e.,
BTEX compounds) are volatilized fairly readily,
and petroleum hydrocarbons are biodegradable
under aerobic conditions.
4.2 Pilot-Scale Testing
Pilot testing should be conducted in a portion of the
target treatment area and should be performed to
determine air sparging feasibility. If the target treatment
area is very large, it may be necessary to conduct pilot
testing in more than one location, particularly if site
soils vary significantly throughout the site. The air
sparging pilot test is designed to: (a) look for indicators
of infeasibility; (b) characterize the air distribution to
the extent practicable; (c) identify unexpected
challenges; (d) identify any safety hazards to be
addressed in the full-scale design; and (e) provide data
to size the full-scale system.
In order to accomplish these objectives, pilot-scale
testing typically includes the following activities:
q Petroleum hydrocarbon source zones often are
relatively small in contrast to a dissolved-phase
plume that may be much larger.
q Petroleum hydrocarbon dissolved-phase plumes
often naturally attenuate readily, and additional
plume control may be unnecessary.
Given these factors, the most economical air sparging
installation may be one that is installed into the source
zone to remove high concentrations of contaminants.
Natural attenuation could then be implemented for remediation of the remaining dissolved-phase plume. If natural
attenuation is not sufficient to control plume migration
before the plume contacts potential receptors, an air sparging system can also be installed at the leading edge of the
plume. This is sometimes referred to as a sparge curtain
or wall.
4.1.2
q Baseline sampling
q Injection pressure and flowrate testing
q Groundwater pressure response testing
Chlorinated Volatile Organic
Compounds
q Soil vapor sampling and off-gas sampling
(with SVE)
For chlorinated solvent contamination, the target
treatment area is influenced by three factors:
q DO measurements
q Helium tracer testing
q Chlorinated solvents such as PCE and TCE
degrade slowly or not at all under aerobic conditions, but are volatilized fairly readily.
q Direct observations
In complex geologic conditions and where well spacing greater than 15 to 20 ft is being considered, additional
tests, such as sulfur hexafluoride (SF6)-distribution testing, neutron probe analyses, and geophysical testing,
may be appropriate. Table 4-1 summarizes pilot-scale
testing activities and the data objectives met by each
activity. A more extensive discussion of pilot-scale
testing activities and implementation can be found in the
Air Sparging Design Paradigm (Leeson et al., 2001).
An Air Sparging Pilot-Scale Testing Activity Matrix is
provided in Appendix G and includes more discussion
of the key issues related to pilot test activities as presented in Table 4-1.
q Chlorinated solvent source zones may be
relatively large and difficult to locate due to the
sinking and spreading of DNAPL in the aquifer.
q Chlorinated solvent plumes often are quite large
because natural attenuation processes are relatively
slow.
Given these three factors, chlorinated solvent source
zone treatment may not be feasible due to a large and/or
unknown location of the source zone. If the contaminant
plume is very large, air sparging may be economically
prohibitive due to the number of wells that would have
to be installed. Therefore, the most appropriate air sparg-
19
q An air supply system consisting of an air filter,
air compressor, and pressure vessel. The air
compressor should be capable of providing at least
20 cfm at pressures up to 10 to 15 pounds per
square inch (gage) (psig) above the calculated
hydrostatic pressure.
TABLE 4-1. Summary of Pilot Test Activities
Activity
Baseline sampling
• Pressure
• DO
• Groundwater
COCs
• Soil vapor
• Geophysical
Injection
pressure/
flowrate test
Groundwater
pressure
response test
Helium tracer test
Soil vapor/SVE
off-gas sampling
Dissolved oxygen
measurements
Direct
observations
SF6 distribution
test
Other geophysical
tools (e.g.,
neutron probes,
electrical
resistance
tomography)
4.2.1
Question(s) Answered
What are aquifer and vadose
zone conditions prior to air
sparging startup?
q Three or more groundwater piezometers or
monitoring wells.
Is it possible to achieve desired
flowrate at safe and reasonable
pressures?
What are the general characteristics of the air distribution?
a) Semiconical air distribution
or
b) Irregular distribution with
preferential channels
What is the lateral extent of the
air distribution? Are there indications of preferential flowpaths?
What is the volatilization rate?
Are there any obvious safety
hazards?
What is the lateral extent of the
air distribution? Are there indications of preferred directions?
Are there any odors, noise, or
other factors present that make
system operation less
acceptable?
What is the vertical and lateral
extent of the air distribution in
the target treatment zone?
What are the oxygen transfer
rates to groundwater?
What is the vertical and lateral
extent of the air distribution in
the target treatment zone?
q Three or more multilevel groundwater/vadose
zone monitoring points.
q A soil vapor extraction system may be needed to
reduce the potential for adverse vapor migration
impacts (or it may be required by regulation). The
SVE system consists of control valves, sampling
ports, air/water separator, air filter, blower, and
vapor treatment equipment.
The air injection well should be designed the same
as wells intended to be used for full-scale implementation (see Section 4.3.1). A typical air injection well is a
1- to 4-inch-diameter vertical well having a 1- to 2-ftlong screened interval installed 5 ft below the lowest
depth of observed contamination. For drilled wells as
opposed to direct-push wells, it is important to ensure a
good annular seal between the top of the screened interval and the water table to prevent vertical airflow within
the borehole.
To the extent possible, existing groundwater monitoring wells and other monitoring installations should be
incorporated into the design. The piezometers and
groundwater sampling points ideally should be screened
only within the target treatment area. Groundwater wells
should be designed and installed such that the length of
screen exposed above the water table is minimized.
Vapor monitoring points should be screened over a
narrow interval (1 to 2 ft maximum) and placed just
above the capillary fringe. Seasonal water table fluctuations should be considered when selecting appropriate
depths for vapor monitoring points. For shallow sites
(i.e., depth to groundwater <30 ft bgs), monitoring networks like these are often quickly and cost-effectively
installed with direct-push methods. At deeper sites, or
sites with access restrictions, practical considerations
may dictate the use of fewer wells or multilevel
samplers.
Pilot-Scale Testing Equipment
Figure 4-1 shows the typical components of an air
sparging system. The following equipment typically is
needed to conduct pilot test activities:
q At least one air injection well equipped with a wellhead pressure gauge, flowmeter, and control valve.
20
FIGURE 4-1.
4.2.2
Components of a Typical Air Sparging System
Pilot-Scale Testing Layout
4.2.3
A sample pilot test layout is shown in Figure 4-2.
When determining the vapor monitoring point layout, it
is important to recognize that air distributions often
have unpredictable preferred directions. Vapor monitoring points should be spatially varied and placed at several different angles from the sparge well because preferential flow and channeling make the air distribution
pattern unpredictable and a straight line of vapor monitoring points might provide inadequate or nonrepresentative data (Bruce et al., 2001). Furthermore, the locations should reflect the hydrogeologic setting and the
preferred well spacing. In most circumstances, the vapor
monitoring points should not be installed more than 10
ft away from the injection well to obtain adequate data
to characterize the injected air distribution. The groundwater monitoring wells should be located at three
different distances, no more than 20 ft out from the
injection well, to obtain good pressure transducer
measurements.
Pilot-Scale Test Evaluation
The data from pilot-scale testing should be evaluated and a decision made about whether or not air sparging is an effective remedial option for the site. The
results of the pilot test can sometimes be a challenge to
interpret because no site will have completely homogeneous flow around an air sparging well. However, the
following is a list of some pilot test results that would
indicate that air sparging is infeasible or less than optimal at a specific site. It should be noted that some of
the following results may also be caused by the
lithology in a highly localized region of the site and the
results of the test could change if the injection point is
moved to a new location.
q If air could not be injected into the aquifer at a
flowrate of 5 to 20 cfm at a pressure that does not
exceed the soil overburden, then air sparging
system design requires more engineering effort.
21
FIGURE 4-2.
Sample Pilot Test Layout
q If mass removal rates during the pilot test are very
low, then there should be considerable concern
about the viability of air sparging at the site. If
pilot sparging wells are placed in high concentration areas, pilot test data typically represent the
maximum achievable removal rate observed over
the lifetime of the air sparging project.
mentability, if buildings and/or other potential
receptors are located nearby.
q Odors caused by the contaminants, noise caused
by the equipment, or other environmental factors
may not make air sparging infeasible from a technical standpoint, but may make the system less
acceptable for the community or property owner.
q If all of the injected air appears to be conducted
through a channel of high permeability based on
tracer testing, then air sparging either may be
infeasible or site-specific system design
enhancements may be necessary to avoid and/or
compensate for this channeling.
4.3 Full-Scale Implementation
If results from pilot testing are favorable, then the
full-scale design may be developed and implemented. If
buildings or underground corridors may be impacted,
vapor migration management must be accommodated in
the system design. This topic is discussed in detail in
Leeson and Hinchee (1996). The engineering design process can be divided into these categories:
q If the groundwater pressures remain elevated for
more than 8 hours, it can be assumed that the
injected air is trapped or limited by subsurface
stratification and may not be reaching the targeted
treatment zone.
q Air injection system
q Vapor extraction and treatment system
(if applicable)
q For sites with SVE systems, if helium recovery is
low (less than 20%), the air is most likely being
trapped by less permeable lenses or layers that
conduct it beyond the SVE system or out of range
from monitoring wells (Figure 4-3). This indication of poor air distribution may impact mass
recovery, but could also limit air sparging imple-
q Monitoring network.
Table 4-2 summarizes the critical design considerations involved in full-scale implementation of an air
sparging installation.
22
FIGURE 4-3.
4.3.1
Helium Tracer Test Results with Optimal and Suboptimal Site Geology
Air Injection System
4.3.1.1
Injection Well Placement
Starting with a plan view map, air injection wells
are placed in locations consistent with the selected well
spacing within the target treatment area. A relatively
dense well spacing of 15 to 20 ft, as shown in Figure 4-4,
is recommended (Leeson et al., 2001; Bass et al., 2000).
The study by Bass et al. (2000) showed that the most
The air injection system is the primary component
of the air sparging system and consists of an air compressor with pressure vessel, air filter, piping, valves/
controls, and injection wells (see Figure 4-1). The following sections discuss injection well placement and
design as well as air compressor selection.
23
TABLE 4-2. Critical Design Considerations for Air Sparging Installations
Installation
Air injection
system
Vapor extraction and
treatment
system
Design Parameter
(a)
Injection well screen begins approximately 5 ft below target treatment area.
Separate pressure control and flowmeter for each injection well.
Competent annular well seal immediately above injection well screen (if drilled installation).
3
3
Flowrate between 5 to 20 ft /min. Note that 20 ft /min has been found to be the most effective.
Pulsed injection in banks of 2 to 5 wells.
Extract 2 to 3 times the volume of air injected and maintain vacuum in soil vapor monitoring points.
If VOC concentrations in the extracted vapor exceed 150 ppmv, consider thermal treatment (i.e.,
thermal or catalytic oxidation). GAC treatment is typically cost-effective for concentrations below
150 ppmv.
Refer to standard design manuals (USACE, 1995).
Option for colocating extraction wells in same borehole as injection wells.
Refer to standard design manuals (USACE, 1998).
Diameter at least 2 inches to allow for insertion of pressure transducer.
Groundwater
monitoring
wells
Multilevel
At least two sampling depths:
groundwater
· In contaminated groundwater area
and vapor
· In vadose zone approximately 1 to 2 ft above water table.
monitoring
Discrete sampling intervals: 0.5 to 1 ft in length and 0.25 to 0.5 inches in diameter.
points
(a) If site stratigraphy does not allow for a separation of 5 ft, the injection screen can be installed at lesser distances
below target treatment zone. However, the shorter the distance from the target treatment zone to the top of the
injection well screen, the greater the chance that portions of the target treatment zone will not receive direct
contact with air channels.
4.3.1.2
Injection Well Design
The critical design parameters for air injection wells
are the depth of the injection well screen, the use of
flowmeters, and the annular well seal. Figure 4-5 illustrates a typical air sparging injection well design.
The vertical air injection well should be constructed
of 1- to 4-inch-diameter, schedule 40 PVC well casing
with a slotted screen. For vertical wells, the well screen
interval should typically be about 1 to 2 ft long and
placed entirely below the groundwater table. Longer
well screens generally are not necessary, but may be
appropriate for some sites where greater air flowrates
are desired and the formation is relatively tight. The
specific screen depth at any given site is based on considerations of the contaminant depth and subsurface
stratigraphy. Performance data demonstrates that placing the top of the injection screen approximately 5 ft
below the bottom of the contaminated zone is preferable
(Leeson et al., 2001). If the source is a DNAPL that
results in dissolved contaminants through the entire
saturated interval, sparging well screens should be
installed such that the bottom of the screen is at or just
above the aquitard underlying the aquifer (assuming
fairly homogenous soils). Injection well screens that are
FIGURE 4-4. Standard Design Approach to
Injection Well Placement
successful air sparging systems consisted of multiple
wells spaced less than 30 ft apart. Typically, a triangulated spacing is preferred because it increases the amount
of overlap of the influence of the individual wells.
24
FIGURE 4-5.
Typical Sparge Well Construction
installed much greater than 5 ft below the target treatment zone run the risk of air bypassing the contaminated
area. Likewise, injection wells installed too shallowly
will likely result in air channels not contacting the lower
portions of the contaminated area. If confining layers
are present, they may prevent airflow from reaching the
contaminants. However, this negative impact can be
avoided by modification of well screen depths or well
spacing. Subsurface stratigraphy may force the practitioner to install the injection well screens closer to the
bottom of the target treatment zone than 5 ft.
25
Vertical Injection Wells
Injection wells should be installed with a competent
annular seal in the borehole above the screened interval,
using a bentonite-and-grout slurry. However, bentonite
chips can be used if hydrated continuously during installation. In the absence of a good seal, the injected air will
flow up along the well bore and the well will be ineffective. At some sites, driven points can be used without
injecting grout; site soils will dictate this use.
The piping and manifolding of the wells need to be
designed such that each injection well has its own dedicated pressure control and flowmeter. This design allows
observation and optimization of airflow into each well,
and unless flow can be regulated to each individual
injection well, air injection will not be uniform throughout the system.
To understand the need for dedicated controls for
each injection well in a network, it is necessary to
understand how airflow is introduced into the saturated
zone. First, a threshold pressure must be attained before
the airflow can push through into the saturated zone.
Enough pressure has to be applied to make room for the
introduced air which involves overcoming the resistance
to airflow contributed by the well screen, the packing
material, the soil matrix, and the groundwater. Once the
threshold pressure is achieved, very small changes in
pressure can result in large flowrate changes (Rutherford
and Johnson, 1996). The minimum pressure needed to
achieve airflow into the saturated zone will be determined during the pilot-scale test. The practitioner should
be aware of the fact that if the minimum pressure
needed to induce flow is too high, there could be safety
issues and practical operational difficulties to air sparging. It is important that the air injection pressure does not
exceed safe levels since high pressures can damage air
sparging well seals and cause fracturing in the formation.
As a general guideline, to maintain the integrity of the
injection well seal, practitioners should proceed with caution when operating in a range near the estimated fracturing pressure (Pfracture). This pressure is related to the
overburden or weight of the soil matrix above the injection point (based on a bulk density of 105 lb/ft3) and can
be estimated with the following theoretical relationship:
Pfracture [psig] = 0.73 × Dsoil [ft]
Air injection wells can be installed using either
direct-push technology or traditional auger drilling techniques. Injection wells installed using direct-push technology tend to be less expensive; however, site soils or
contaminant depth may necessitate the use of traditional
auger drilling techniques.
Direct-push techniques are believed to minimize
disturbance of the soil column and to eliminate the need
for well packing material. In less permeable soils, sand
pack installation and grouting below the water table
may be necessary to prevent short-circuiting. If site conditions are suitable, direct-push is quicker than
traditional auger drilling.
Direct-push wells are typically small diameter wells
with pre-packed well screens. Air sparging injection
wells can be constructed with standard off-the-shelf
groundwater well systems. These pre-packaged systems
are available in two sizes: 1.4 inches OD (outer
diameter) (0.5 in or 0.75 in ID [inner diameter]) and 2.5
inches OD (1.0 in or 1.5 in ID). The pre-packed well
screens typically consist of 20/40 grade sand. The small
diameter well has a 0.50-inch Schedule 80 PVC riser
and is installed with a 2.125-inch OD probe rod. The
large diameter well uses a 1.0-inch Schedule 40 PVC
riser pipe and is installed with a 3.25-inch OD probe
rod. The wells are lowered to the required depth after
the probe rod has been driven into the subsurface to the
target depth. Once the well assembly has been lowered,
and the probe rod retracted, a sand barrier is created
directly above the well screen, which prevents grout
from entering the screen. A granular bentonite or
bentonite slurry is then installed in the annulus and the
well is sealed and grouted according to EPA and ASTM
D-5092 method requirements. Standard aboveground or
flush-mount well protectors can be used with direct
push wells.
If site geology and/or contaminant depth prevent the
use of direct-push techniques, other drilling methods,
such as hollow-stem augering, will be required. When
using a hollow-stem auger, it is vital to have a good
annular seal that begins well below the water table.
Whenever possible, the diameter of the borehole should
be at least two times greater than the sparging well outside diameter. The annular space corresponding to the
screened interval should be filled with silica sand or
equivalent. The annular space above the screened interval should be sealed with a bentonite-and-grout slurry to
prevent short-circuiting of air to the vadose zone.
(4-1)
where: Dsoil [ft] = depth below ground surface to the top
of the air injection well screened interval. The actual
fracture pressure of the formation may be greater due to
the resistance offered by friction along the margin of the
overburden column and resistance offered by surface
completion features (e.g., concrete pad).
26
Existing groundwater monitoring wells are unlikely
to be suitable for use as an injection well. Groundwater
monitoring wells are frequently screened above the
water, or may at least have a sand pack that extends
above the water table. In these situations, the majority of
the injected air will be delivered into the vadose zone
with little or no air entering the saturated zone outside
the borehole.
and reciprocating piston-type compressors are suitable
for air sparging applications. Reciprocating piston air
compressors are typically designed to deliver low flow
at higher pressures than rotary vane compressors, so
they can be used for sparging at deep sites or in low
permeability soils. Figure 4-6 shows a typical performance curve for a 5-hp reciprocating piston air compressor.
Air compressors should be selected based on their
ability to deliver the desired flow at a pressure that does
not exceed 60% to 80% of the maximum pressure. The
empirical data collected during pilot testing should be
used to properly size the compressor for full-scale use.
Proper sizing and selection of a compressor is essential
to ensure that the unit can deliver the required airflow at
the necessary pressure and that it operates properly.
Choosing the wrong compressor can result in an inability to deliver sufficient air or a significantly shortened
compressor life. It is best to select the compressor to
allow operation near the middle of its performance range.
A compressor operating near its maximum pressure is
running inefficiently and under stressed conditions,
thereby increasing operating costs and shortening its life.
Selection of an oversized compressor reduces operating
efficiency and increases design and installation costs
unnecessarily.
Practitioners have varied opinions on the effect of
changing air injection flowrates. Some believe that lower air injection rates favor biological treatment relative
to volatilization, while others believe that increased injection rates can improve air distribution. Johnson et al.
(2001) states that low air flowrates generally yield less
extensive air distributions compared to high air flowrates.
Laboratory-scale studies (Ji et al., 1993; Rutherford and
Johnson, 1996) indicate that increasing the injection
flowrate results in positive effects, especially in stratified geological settings, by allowing the air to break
through soil layers under which it might normally be stratified, creating a dense air distribution network. Although
a high injection rate is favorable, it will undoubtedly
result in higher costs due to the necessity of selecting a
larger compressor. The practitioner must weigh all these
factors when selecting a compressor.
Horizontal Injection Wells
Horizontal wells are occasionally installed to inject
air below structures within or through which drilling is
not possible. However, horizontal wells have the disadvantage of higher installation costs and a high potential for nonuniform aeration. Wade et al. (1996) documents the difficulties with non-uniform aeration during
the use of a 200-ft horizontal well as a barrier to the
migration of a chlorinated solvent plume, although relatively successful implementations have been documented
(Kershner and Theoret, 1997; Roth et al., 1998). Horizontal well installation for air sparging is not typically
recommended.
4.3.1.3
Air Compressor Selection
An air compressor provides the driving force to
move air through the sparging system. Compressors typically are selected during the pilot-testing phase based
on expected injection flowrates and pressure requirements. According to current design practices, the practitioner should expect to inject air at flowrates ranging
from 5 to 20 cfm per injection well at pressures 10 to
15 psig above the hydrostatic pressure. Compressor
selection should be discussed with a reputable vendor
and/or manufacturer. It is important that the unit(s) be
capable of: (a) providing the necessary flow capacity of
clean air at the design pressures, and (b) long-term continuous operation with minimal maintenance requirements. In selecting the compressor size, one must
consider the required air flowrate and the total system
pressure drop. System pressure drop includes the backpressure due to the injection wells and formation in an
air injection configuration plus any pressure drop in the
system piping. Both oil-less, rotary vane compressors
27
FIGURE 4-6.
4.3.2
Example Air Compressor Performance Curve
Vapor Extraction and Treatment
System
typical components of an SVE system include the
vacuum blower, air filter, air/water separator, valves/
controls, extraction wells, and vapor treatment system
(see Figure 4-1).
The soil vapor extraction rate should typically be 2
to 3 times the air injection rate and should maintain
adequate vacuum in the nearby soil vapor monitoring
points. The number of SVE wells required will typically
be less than the number of air sparging wells because
the spacing for SVE wells is generally on the order of
30 ft or more, compared to the 15-ft spacing for a standard air sparging design. The minimum number of SVE
wells required can be estimated by the ratio of target
treatment area to the area of influence of the SVE well
as follows:
Vapor extraction systems are installed in conjunction with in situ air sparging systems when contaminant
vapors must be recovered, or where there is concern that
contaminant vapors could migrate to enclosed spaces
(e.g., utility conduits, basements, buildings). An SVE
system should not be installed when vapors, particularly
petroleum hydrocarbon vapors, can be degraded in the
vadose zone. In general, if safe and feasible, air injection into the aquifer with no SVE is the preferred and
most economical configuration for full-scale air sparging systems. However, several conditions may require
vapor collection and treatment:
q One or more of the target contaminants are not aerobically biodegradable (e.g., chlorinated solvents).
NSVE =
q Soil vapor monitoring indicates that contaminants
are not adequately biodegraded in the vadose zone
and could potentially impact utility conduits,
basements, and/or buildings.
A target
π(R SVE )2
(4-2)
where: NSVE = minimum number of SVE wells
Atarget = target treatment area
RSVE = radius of influence for SVE well.
q Substantial contaminant mass remains in the
vadose and/or smear zone through which the water
table fluctuates (typically this condition exists in
or near the source area).
The radius of influence for SVE wells is typically
around 20 ft for sandy/silty soil types and 30 ft or more
for sand to gravel soil types.
The SVE wells can be located adjacent to an air
sparging well or in between a network of air sparging
wells. An additional option for SVE well placement is
to colocate the extraction well and air sparging injection
well in the same borehole. This strategy provides a
SVE systems are routinely installed and design considerations are covered thoroughly in several manuals
(including U.S. Army Corps of Engineers, 1995). The
28
conservative SVE well spacing, but will reduce installation costs.
Figure 4-7 is a diagram of a typical SVE well. The
SVE wells should be screened above the seasonal high
water table to avoid flooding of the wells. The SVE well
should be constructed of 2- to 4-inch-diameter, schedule
40 PVC well casing with a slotted screen. After the
screen and riser are installed, the annular space is filled
with a silica sand mixture to a height of 2 ft above the
screen. A 2-ft-thick (minimum) bentonite seal is placed
on top of the sand pack and the remaining annular space
filled with a bentonite-cement grout mixture. A flushmount protective vault with a watertight, locking well
cap is often placed over the well.
There are several options for the vapor treatment
system such as: thermal oxidation, catalytic oxidation,
and granular activated carbon. Thermal oxidation and
catalytic oxidation rely on thermal destruction to combust the contaminants and convert them to carbon dioxide and water, while granular activated carbon relies
upon adsorption of the contaminants onto a carbon substrate for later regeneration and/or disposal. If VOC
concentrations in the extracted soil vapor exceed
150 ppmv, consider thermal oxidation or catalytic oxidation. Granular activated carbon is generally costeffective for concentrations below 150 ppmv. However,
each constituent has a different adsorption capacity
ranging from 1.5g/100g GAC for VC to 54g/100g GAC
for PCE. Catalytic oxidation is typically not suited to
sites with chlorinated volatile organic compounds.
4.3.3
interval of the monitoring wells is filled with a mediumgrade silica sand filter pack. The remaining annular space
is sealed to the surface with a bentonite plug. A minimum
well diameter of approximately 2 inches is required for
use of most pressure transducers. Other design parameters of a standard groundwater monitoring well will
allow for collection of pressure and contaminant data.
The following issues should be considered regarding the
use of groundwater monitoring wells:
q The location of groundwater monitoring wells
should span the system treatment area from
upgradient, through the treatment area, to downgradient of the area.
q Downgradient wells should include at least one
sentinel well just upgradient of a defined compliance point.
q The number and distribution of wells upgradient
and within the treatment area is specified by the
project context and site conditions.
q Groundwater monitoring wells should not be used
for measuring parameters such as dissolved oxygen or tracer gases, because results can be affected
by well screens that extend above the water table
(Leeson et al., 2001).
4.3.3.2
Monitoring points are used for groundwater and soil
vapor measurements and are a very important component of an air sparging system. Figure 4-8 is a diagram
of a typical multilevel groundwater and soil vapor monitoring point. Proper construction of monitoring points is
essential for monitoring groundwater and soil vapor
concentrations.
Each monitoring point should be screened at a
minimum of two depths. The deepest sampling screen or
port should be located in the saturated zone within the
target treatment area. The sampling ports should be
placed in the aquifer at depths within which most of the
dissolved contamination is located as determined by site
characterization (sampling and lithology) and permeability test data. Because air distribution and contaminant
migration are very sensitive to site-specific conditions,
sampling port placement must be determined on a sitespecific basis. The objective of the location is to be
situated in the target treatment area and to facilitate
tracking of the performance of the air sparging system
in situ.
Monitoring Network
The monitoring network for an air sparging system
consists of groundwater monitoring wells and multilevel
monitoring points. Groundwater monitoring wells are
traditional wells with a relatively large screened interval
(approximately 5 ft) in the contaminated zone of the
aquifer. Multilevel monitoring points are much smaller
and are designed to collect water and soil vapor samples
from discrete intervals in the groundwater and vadose
zone.
4.3.3.1
Multilevel Monitoring Points
Groundwater Monitoring Wells
Construction of groundwater monitoring wells is
standardized and often dictated by local regulatory
issues, and is defined in detail in several manuals
(including U.S. Army Corps of Engineers, 1998). A
typical groundwater monitoring well may consist of
4-inch-diameter PVC casing with the well screen in the
saturated zone. The annular space outside the screened
29
FIGURE 4-7.
Typical SVE Well Construction
Depth intervals may be determined from historical site
data or a preliminary groundwater survey. At least one
sampling port should be located in the vadose zone 1 to
2 ft above the water table to monitor contaminant vapor
concentrations. In some cases, it may be desirable to add
additional screened depths to more fully monitor the
contaminated interval, to monitor differing stratigraphic
intervals, or to adequately monitor deeper sites.
Soil vapor monitoring point construction will vary
depending on the drilling depth and technique. If traditional auger drilling is being used, a simple construction
technique is to use small-diameter (1/4 inch) tubes
extending to the specified depth in the vadose zone,
30
FIGURE 4-8.
Typical Soil-Vapor/Groundwater Monitoring Point Construction
with a screen approximately 6 inches long and 1 inch in
diameter attached to the end. In shallow open-hole
installations, rigid tubing terminating in the center of a
gravel or sand pack may be adequate. The gravel or
sand pack normally should extend for an interval of 1 to
2 ft, with the screen centered. In low-permeability soils,
a larger gravel pack may be desirable. In wet soils, a
longer gravel pack with the screen near the top may be
desirable. A bentonite seal at least 2 ft thick normally is
required above and below the gravel pack. The
following issues should be considered regarding
multilevel monitoring points:
q Monitoring points should be distributed
throughout a site to adequately measure contaminant concentrations.
q A sufficient number of monitoring points should be
installed to ensure representative sampling. The
actual number installed is site-specific and is driven
31
primarily by plume size, the cost of installing and
monitoring additional monitoring points, the scope
of the project, and regulatory considerations.
oxygen and contaminants. The tubing material
must have sufficient strength and be nonreactive.
Appropriate materials include nylon and Tygon™.
Sorption and gas interaction with the tubing
materials have not been significant problems for
this application. If a monitoring point will be used
to monitor specific organics in the low-ppm or
low-ppb range, Teflon™ or stainless steel tubing
may be appropriate.
q Monitoring points must be located between the
injection well and any buildings that may be at
risk to ensure that the structures are not impacted
by vapor-phase contaminants.
q Monitoring points typically are used to collect
groundwater and soil vapor for measurement of
32
5.0 SYSTEM OPERATION, MONITORING, AND OPTIMIZATION
Operation, monitoring, and optimization efforts must
be focused on specific remedial objectives. Generally,
these objectives include maximizing mass removal efficiency with respect to both time and money, minimizing
O&M costs, and achieving site closure. This section outlines system startup, operation, and monitoring recommendations that can be applied toward project-specific
objectives. A troubleshooting guide for air sparging system operation is presented in Appendix H.
Components to be checked include the air compressor; in-line airflow meters and pressure
gauges; groundwater and soil vapor monitoring
points; groundwater analysis instrumentation; soil
vapor analysis instrumentation; SVE system (if
applicable); and any vapor treatment system components. A site-specific checklist should be used
to document the system shakedown (see Table 5-1).
q If the air sparging system is coupled to an SVE
system to collect vapors stripped from the groundwater, then the SVE system should be operated for
a period of time prior to air sparging startup to (1)
ensure that the SVE system is operating properly;
(2) help dry the soil, increase vadose zone permeability, and maximize SVE capture efficiency; and
(3) capture the initial high mass loading from air
sparging. Note that if the SVE system is installed
in an area having impacted unsaturated soil (such
as near the source release or an area where the
water table elevation fluctuates over a wide
5.1 System Startup
The objectives of performing system startup checks
are to ensure that the system was designed, installed,
and assembled properly, that continued operation of the
system will not result in safety hazards or equipment failures, and that preremediation conditions are well understood. Typical startup activities are as follows:
q A brief startup test must be conducted to ensure
that all system components are operating properly.
TABLE 5-1. Air Sparging System Startup Checklist
System Component
Compressor shutoff
switch
Compressor tank relief
valve
Primary pressure
regulator
Primary flow valve
Manifold system (to
split airflow to multiple
sparging wells)
In-line pressure gauge
In-line flowmeter
In-line check valve
In-line flow valve
Air line hoses, fittings,
connectors
Sparging wellhead
Evaluation Criteria
Ensure the proper function of this safety feature. This switch shuts off delivery to the reservoir at
the target pressure. Follow manufacturers’ instructions.
Ensure the proper function of this safety feature. This valve exhausts air from the reservoir if the
internal pressure exceeds safety limits (in the event the shutoff switch fails). Follow
manufacturers’ instructions.
Check to ensure that the pressure delivered from the reservoir can be adjusted within the range
of intended operating pressures.
Check to ensure that the flow from the reservoir can be immediately terminated by closing this
valve.
Check to ensure that there are no air leaks from the manifold and that connections to sparging
well lines are secure.
Check to ensure that the pressure in each sparging line can be adjusted and that the air flowrate
responds to changes in pressure within the safe range of operating pressures.
Check to ensure that there is no debris or obstruction in the meter that would impede its proper
function. Check that air flowrate changes with pressure adjustments within the safe range of
operating pressures.
Ensure that check valves are in place if cyclical operation of some or all sparging wells is
expected. (Under some conditions check valves may not be necessary.)
Check to ensure that flow to each individual sparging well can be immediately terminated by
closing each valve.
Check to ensure general integrity and secure fittings and connections. Damaged hoses and
fittings should be replaced immediately upon observation.
Check to ensure that excessive pressure is not damaging the wellhead and surrounding seal.
Ensure that access to wellhead fittings is maintained.
33
q Studies suggest that mass removal can be
increased by 20% to 30% through pulsed operation (Bruce et al., 2001, Kirtland and Aelion,
2000).
range), the mass removal rate achieved by volatilization from the vadose zone may dominate the
additional mass removal rate added by starting air
sparging and may not be noticeable using field
instruments. For example, using typical sparging
and extraction air flowrates and a generous estimate of in situ stripping efficiency, 1,000 mg/L of
benzene in groundwater would result in an SVE
off-gas concentration of about 25 ppmv (assuming
the extraction flowrate is twice the injection
flowrate). Initial SVE off-gas concentrations
without air sparging can be greater than
10,000 ppmv, and may therefore mask any contribution from air sparging once that airflow stream
is initiated.
q The difficulty of controlling a multiwell air
injection system increases as the number of wells
manifolded together increases.
q The total required system injection flow capacity
is lower in pulsed mode, resulting in lower costs
for air compressors.
q Pulsed operation may be necessary in sparge
barrier applications to prevent groundwater
bypassing due to water permeability reductions in
the formation caused by air injection.
q If an SVE system is not part of the air sparging
system, then soil vapor concentrations (including
contaminant and oxygen concentrations) should be
measured. The initial baseline contaminant
concentrations in the vadose zone should be
measured and compared to the levels observed
after startup. An increase in contaminant soil
vapor concentrations can then be attributed to
volatilization from the groundwater. Initial oxygen
concentrations are useful for measuring bioactivity
in the vadose zone. Field instruments, as opposed
to more costly laboratory analysis, should be
appropriate for this purpose.
The most effective cycling frequency is site-specific
and depends on the characteristics of site soils and the
distribution of the dissolved contaminants. To date,
there is little guidance on how to choose pulsing frequencies (defined by on and off times). SVE system
data provide a direct measure of volatilization removal
rates, and therefore can be used to assess how changes
in pulsing conditions affect volatilization rates. Some
practitioners believe that the minimum injection period
(the on times) for air sparging should be consistent with
transient pressure transducer response data identified
during pilot testing. Air injection needs to last at least as
long as the time necessary to reach the peak in transducer
response, and preferably as long as the time required for
pressures to return to near equilibrium or asymptotic
values. This indicates that the injected air has emerged
from the aquifer into the vadose zone, and near steadystate flow conditions have been achieved (Johnson et
al., 2001).
q To initiate air sparging, the air flowrate should be
increased slowly to the desired flowrate in order to
ensure that the pressure does not exceed the maximum pressure and prevent damaging the well seal
or fracturing the soil. As groundwater is temporarily displaced after the initiation of sparging,
backpressures and flowrates are likely to fluctuate.
This variable period is typically short-lived as air
channels are formed allowing sparged air to reach
the vadose zone.
5.3 System Performance Monitoring
The general objectives of system monitoring are to
provide current information regarding progress toward
remedial objectives. System monitoring provides the
opportunity to maintain contaminant removal efficiency,
improve operation strategies, track progress toward remedial goals, and stop operations when cost efficiency is
lost or remedial goals are achieved. A monitoring plan
containing data objectives, monitoring parameters, locations, and frequencies should be developed and agreed
upon by the site managers and regulators to ensure that
5.2 System Operation
Air sparging systems can be operated in either a
continuous or pulsed mode, but cycling air injection in
each well intermittently is thought to achieve more
extensive air distribution. Cyclical or pulsed operation
of banks of two to five injection wells is recommended
for the following reasons:
34
q Average treatment cost per pound of VOC
recovered vs. time.
these goals are met. Appropriate quality assurance (QA)
procedures should be followed in developing and implementing this plan to ensure that valid data are collected
and analyzed.
Regardless of the air sparging system design, it is
essential to include one or multiple wells for monitoring
contaminants on the upgradient side of the air sparging
system. Upgradient wells can provide an early warning
of potential plume breakthrough if, over time, the plume
develops in such a way that influent concentrations exceed those planned for in the design.
5.3.1
5.3.2
Estimating Contaminant Removal
SVE off-gas concentrations should be monitored
regularly for VOC levels and volumetric flowrate to
estimate and track the mass of VOCs removed by the
SVE system. The mass removal rate at the time of monitoring can be estimated using Equation 5-1:
æ 1 kg ö
÷
mSVE = C × Q çç 6
÷
è 10 mg ø
Operation Parameters
During continued operation, the following measurements should be made on a periodic basis (ranging from
weekly to semiannually):
(5-1)
where: mSVE = mass removal rate in the SVE off-gas
stream, kg/day
C
= concentration of VOCs in SVE off-gas
stream, mg/m3
Q
= volumetric flowrate in SVE off-gas
stream, m3/day.
q Air sparging system injection flowrates (weekly)
q SVE system inlet and outlet concentrations (as
required by the air discharge permit) and flowrate
monitoring (weekly)
The total VOC mass removed (mSVE) in the SVE off-gas
stream can be estimated using Equation 5-2:
q System controls that regulate cycling (monthly)
q Groundwater quality monitoring of dissolved
oxygen and contaminant concentrations (quarterly
to semiannually as required by regulatory
guidelines)
M SVE =
n
åC×Q × t
i =1
where: C
q Groundwater level measurements in wells
unaffected by air injection (seasonal) to assess the
position of the groundwater table relative to the
injection and extraction wells’ screened intervals
Q
i
n
ti
q Soil vapor VOCs, oxygen, and carbon dioxide
(quarterly to semiannually).
RPMs should ensure that enough data is available to
track the performance and cost trends of the air sparging
system. The following recommended plots should be
developed and incorporated into reports to track system
performance of an air sparging system with SVE:
i
æ 1 kg ö
÷
× çç 6
÷
è 10 mg ø
(5-2)
= concentration of VOCs in SVE off-gas
stream, mg/m3
= volumetric flowrate in SVE off-gas
stream, m3/day.
= counting variable
= total number of time periods summed
= time intervals over which the
concentration and flowrate data are
taken to be representative, days.
To calculate the VOC concentration in mass per unit
volume from parts per million by volume (as are common units in field instruments), Equation 5-3 can be
used (at 25°C):
q Influent VOC concentration vs. time
0.041
1 ppmv =
q Cumulative mass recovered vs. time
mg
m3
unit MW
(5-3)
For example, if the off-gas temperature is 25°C and
the relative concentration weighted average molecular
weight (MW) of VOCs in the off-gas stream is 80, then
q Cumulative treatment costs vs. cumulative VOCs
recovered
35
1,000 ppmv would convert to 3,280 mg/m3 in units of
mass per unit volume by the following equation:
be drawn between operational monitoring collected to
provide information to help maintain efficient operations and data collected for regulatory compliance. The
following suggestions apply to improving groundwater
monitoring implementation:
mg
æ
ö
ç
÷
3
m
÷
80 (MW) × 1,000 (ppmv) × 0.041 ç
ç MW × ppmv ÷
ç
÷
è
ø
mg
= 3,280 3
m
(5-4) q The chemical parameters that typically are
measured in the monitoring wells include concentrations of contaminants and potentially toxic
byproducts. Sampling and analytical techniques
for monitoring wells located in the aquifer are
If no SVE system is employed, contaminant mass
similar to those for site characterization. Groundremoval can be measured in situ or estimated based on a
water sampling can generally be done with an
simple aerobic biodegradation equation (Leeson et al.,
appropriate length of Teflon™ tubing and a peri2001) as follows:
staltic pump. At deeper sites (>30 ft [9 m]) a
submersible pump or a bailer may be required to
103 L 10-6 kg 0.33kg - HC
lift water to the surface. The methods used to
(5-5)
R gw = Vsoil × n × O × 3 ×
×
collect and analyze groundwater should be clearly
mg
kg - O 2
m
defined in the monitoring plan. Guidance documents are available to help practitioners develop
where: Rgw = aerobic biodegradation rate of contamtechnically sound and cost-effective monitoring
inant in groundwater due to oxygen
plans including NFESC’s Guide to Optimal
delivery to groundwater (kg/day)
3
Groundwater Monitoring (NFESC, 2000a).
Vsoil = volume of treatment zone (m )
n
= porosity of aquifer (L-pores/L-soil)
q Because monitoring costs constitute a major
O = dissolved oxygen delivery rate to
annual operating cost of the air sparging system
groundwater outside of air channels
for several years after construction, site managers
(mg-O2/L-water/d).
should optimize both the number of monitoring
wells sampled and the information gained. Data
5.3.3 Compliance Monitoring
objectives must be clearly identified in the monitoring plan and agreed upon among the project
Compliance monitoring for an air sparging system
team (project manager, contractor, and regulator).
typically involves the collection and analysis of both
Adequate site characterization in the vicinity of
groundwater and soil vapor samples. Compliance monithe proposed air sparging system, as well as
toring allows a practitioner to track the air sparging syshydrologic modeling, can assist both project mantem performance and the progress made towards meetagers and regulators in determining the appropriate
ing cleanup goals and performance objectives.
number and locations of monitoring wells to
install at a given site.
5.3.3.1 Groundwater Monitoring
The frequency of compliance monitoring should be
determined with the regulators prior to system startup.
Discussions should focus on eliminating unnecessary
data (type and quantity) that do not help meet specific
data objectives. Quarterly monitoring typically is required during operations in order to minimize uncertainty related to impacts from seasonal hydrologic conditions. However, after the system has been shut down
and rebound has been determined to be insignificant,
less frequent monitoring (biannual or annual) can confirm that concentrations continue to decrease or are consistently below remedial objectives. Distinctions should
q Cost minimization is most effectively achieved by
focusing on the monitoring data objectives. It is
very common to collect data in greater quantity, at
a greater frequency, and at more locations than are
actually used to interpret plume behavior. Collecting excess data should be avoided if at all possible.
q Minimizing levels of investigation-derived waste
(IDW) is another way to reduce costs. Applicable
regulations and guidance documents should be
reviewed to determine if alternative well purging
techniques are permissible at the site. For
36
example, micropurging techniques (Kearl et al.,
1992) and diffusion samplers (Vroblesky and
Campbell, 2000) are becoming more generally
accepted and can reduce both IDW and the cost of
handling, treatment, and disposal.
5.3.3.2
can be achieved in less than six months (Bass et al,
2000). Figure 5-2 shows an idealized plot of cumulative
mass removed over time. Note that the majority of the
mass is removed in the initial stages of operation and
that every equivalent time interval thereafter produces
greatly diminishing removal rates. This behavior results
in a remediation system that is achieving a mass
removal rate substantially less than that for which it was
designed, typically the maximum rate observed soon
after system startup. The following issues should be
addressed during the design or optimization phase in
order to ease transition of the system to final shutdown:
Soil Vapor Monitoring
It is common for air sparging systems to be regulated under an air discharge permit to protect against
harmful vapor discharges to the atmosphere, even if the
system is not coupled with an SVE system. In an airsparging-only system, periodic monitoring of shallow
soil vapor or ambient air just above ground surface may
be required to ensure against excessive discharges of
VOCs. Typically, air injection will result in only minimal emissions to the surface (U.S. EPA, 1992). Soil
vapor monitoring options include sampling from shallow soil vapor monitoring points into Tedlar™ bags or
evacuated polished metal canisters, or the use of vaporphase diffusion samplers. Typically, laboratory analysis
of vapor samples is required because the quantitation
limits achieved by field meters cannot satisfy data
objectives for regulatory compliance. However, handheld, direct reading instruments are useful for
operational monitoring.
q Focus strategic sparging well placement on localized areas with elevated contaminant concentrations or the plume centerline. This approach can
greatly reduce the cost of installation (compared to
complete plume coverage) without substantially
increasing operating time.
q Reduce the design capacity of air supply, vapor
extraction, and vapor treatment units. This
approach will reduce the maximum mass removal
capacity of the system, but will result in a system
that operates near its optimum design capacity
(60 to 80% of maximum capacity) for a longer
duration. (Note that the trade-off of lower capital
equipment expenses could extend the time
required to achieve active remediation goals and
should be evaluated accordingly. Reducing maximum removal capacity does not necessarily extend
the required time of remediation, but it may.)
5.4 System Optimization
The objective of system optimization is to achieve
remedial goals with a minimum investment of time and
money. Understanding the likely or typical behavior of
these systems can provide opportunities to reduce costs
in the initial design phase, and throughout the life of the
project. The practitioner should review current monitoring data and look for opportunities to improve
removal efficiency such as optimizing air flowrates and
sparge well placement. Figure 5-1 is a flowchart showing
a remedial action optimization process for air sparging.
The experience of the environmental remediation
industry, case histories of previously installed and operated air sparging systems, and knowledge of pertinent
mass transfer mechanisms all can be incorporated into
the design, installation, operation, optimization, management, and exit strategies for an air sparging project. It is
expected that after a variable plateau period of maximum
mass removal rates (possibly ranging from nonexistent
to several weeks), the mass removal rate will rapidly
decline over time as mass reaching the air/water interface comes from sites farther away from the injection
wells and air channels. Literature has shown that significant mass removal for BTEX compounds (96-98%)
q Consider constructing air supply, vapor extraction,
and vapor treatment units on mobile trailers. This
approach has been used at many installations to
reduce the fixed costs of equipment and enable the
equipment to be reused at other sites on an installation. Furthermore, the air supply and extraction
equipment can be employed for multiple uses
(beyond air sparging and soil vapor extraction).
Typically these equipment items can be considered
to have service lives of approximately five years,
depending on their size, quality, and rate of use.
5.4.1
Evaluation of Cleanup Goals and
Performance Objectives
Cleanup goals and performance objectives should
be evaluated periodically to review the regulatory history, review the current and future land use plans, and
evaluate the need to revise goals.
37
REMEDIAL ACTION OPTIMIZATION (RAO)
PROCESS FOR AIR SPARGING SYSTEMS
•
•
•
•
• Review Regulatory History/Cleanup Goals
• Review Current and Future Land Use Plans
• Determine Process for Revising Cleanup Goals
• Evaluate Whether Engineering/Institutional
Controls Can Protect Receptors
• Develop and Propose Risk-Based Cleanup
Goals and Enforceable Land Use Controls
Can
Existing
Remedial System
Achieve Cleanup
Goals Within
2 Years at a
Cost of
<$100K/year
?
No
No
Yes
Continue Operations and Phase I Optimization
38
If Appropriate, Propose
Revised Goals
Evaluate Source Isolation/Plume
Containment Regulatory Options
Including Technical Impracticability
Alternate
Isolation/
Containment
Goals
Accepted
?
No
Appeal Regulatory Decision
No
Yes
Can
(Optimized or
New) Remedial
System Achieve
Cleanup Goals
Within Reasonable
Time Frame
?
• Implement Source Isolation/Plume
Containment System(s)
Yes
Review Feasibility Studies/Remedial Designs
Review Available Performance Data
Compare Actual vs. Predicted Performance
Estimate Time Frame to Achieve Existing
Cleanup Goals
• Evaluate Potential for System Optimization
• Evaluate Potential for Integrating Monitored
Natural Attenuation into Remediation Strategy
• Evaluate New/Proven Alternate Technologies
• Develop Optimized Long-Term Monitoring Strategy
• Compare Optimization of Existing System to New
Technology Replacement Options and Select Most
Effective System/Cost vs. Benefit Analysis
• Reevaluate Time to Achieve Original or Revised
Cleanup Goals
Implement (Optimized or
New) Remediation System
• Establish Performance Objectives
and Performance Indicators
• Continue to Perform Periodic
System Monitoring
• Develop Statistical Evidence
for Site Closure
• Continue to Evaluate
Emerging Technologies
• Continue to Evaluate Regulatory
Framework While Optimizing
Existing System
Modified from AFCEE, 1999
FIGURE 5-1.
System Optimization
Remedial Optimization for Air Sparging Systems
Continue Annual Evaluations or
Proceed to Site Closure
PTFLOW01.CDR
Evaluation of Cleanup Goals
pathways, or zones of greater permeability connected to
the source zones. Mass removal is likely to be most
effective in these same zones; therefore, air sparging
activity should focus on these areas, if they can be
identified. In the absence of an SVE system, monitoring
the relative concentration of VOCs in soil vapor may
provide insight regarding which sparging wells are most
effectively stripping contaminants from zones of higher
concentration. In addition, these preferential pathways
also result in greater flowrates at lower injection
pressure due to less frictional headloss in the formation
itself. Elevated VOC concentrations in soil vapor
indicate that the subject air sparging well(s) is in a good
location for effective removal.
FIGURE 5-2. Typical Behavior of an Air
Sparging System
5.4.3
5.4.2
Optimizing Airflow
Optimizing Well Placements
Although adequate site characterization data should
be collected prior to the design of a site-specific air
sparging system, inevitably more information regarding
the extent and distribution of contaminants is gained as
system operation and monitoring proceed. This
information can be used to improve mass removal
efficiency by adjusting the system design in accordance
with the new information. For example, groundwater
monitoring and soil vapor data can be used to identify
areas between sparging wells (or outside their area of
influence) where reservoirs of contaminant mass are
only minimally affected by the sparging activity.
Placing a few additional sparging wells in these areas
can substantially accelerate removal and decrease the
time to system shutdown. Figure 5-3 illustrates how
focused well placements can improve VOC recovery
rates. Helium tracer tests also can be used to identify
dead zones between sparging locations; if dead zones
are identified, additional sparging wells should be
installed. Additional site characterization such as soil
borings, groundwater wells, or other activities may
reveal new sources or areas with elevated contaminant
concentrations, and additional sparging wells can be
added to increase airflow to these areas. Also, operators
should continuously explore opportunities to shut off
airflow and possibly abandon inefficient sparging wells
located in areas of low concentration or tight deposits.
The objective of optimizing airflow is to maximize
mass removal. Typically, mass removal is maximized in
homogeneous deposits by an approximately uniform distribution within the treatment area matching the likely
distribution of contaminants. In heterogeneous deposits,
contaminant distribution is more likely to be
concentrated in zones of greater permeability. Focusing
sparging activities in these areas of greater permeability
is likely to be an efficient way to maximize removal.
Once the desired flowrate is achieved in a single
injection well, a practitioner then can begin balancing
the flow to all injection wells operating within the well
bank. It can be difficult to achieve the same flowrate in
all injection wells within the same well bank. Adjusting
flowrates to ±2 cfm from the desired flowrate is
reasonable. Balancing of flows will have to be repeated
for each well bank. Flowrates should be checked and
minor adjustments made through several air injection
cycles. In general, checking flowrates frequently during
the first two weeks of operation should be sufficient to
ensure stable flowrates.
In heterogeneous deposits, contaminant distribution
and achievable air flowrates will be determined by the
relative permeability of the deposits in the target treatment area. For example, the most significant migration
of dissolved contaminants will occur in preferential
39
FIGURE 5-3.
Optimized Well Placement in High Concentration Areas
40
6.0 SYSTEM SHUTDOWN, LONG-TERM MONITORING, AND SITE CLOSURE
When cleanup goals have been attained or when
continued operation of the air sparging system is no
longer cost-effective, it is appropriate to terminate system operation. System shutdown should generally be
accomplished after 6 to 18 months of full-scale operation (Bass et al., 2000). Following system shutdown,
it will likely be necessary to perform postremedial
long-term monitoring to evaluate contaminant rebound
and plume stability prior to obtaining site closure.
As part of the exit strategy, the air sparging system
should remain in place for at least one year after system shutdown in case contaminant rebound requires
additional operation. Poor performance at air sparging
sites can often be attributed to a rebound in VOC concentrations occurring six months to a year after the
system has been shut down. Bass et al. (2000) determined that rebound was found to be particularly prevalent at petroleum hydrocarbon sites where a LNAPL
smear zone was present and the seasonal fluctuation of
the water table exposed the groundwater to new
sources of contamination.
6.1 System Shutdown
At some sites the air sparging system will reduce
contaminant concentrations sufficiently to meet the
cleanup goals. However, at other sites the air sparging
system will reach an asymptotic level of mass removal
prior to achieving the cleanup goals. In these cases,
alternative approaches, such as monitored natural attenuation, should be considered to attain final cleanup
requirements. The political and regulatory context must
be considered in making the decision to shut down the
system and switch remedial strategies, but incorporation of this expected outcome from the early stages
of the project can facilitate the change when it is
appropriate. In addition, a cost-effective remedy is
commonly mandated by regulation, and the system
operation data may be presented as evidence that
active remediation is no longer cost-effective. Incorporating the expected behavior of the remediation system
into the project management and system design will
reduce project costs and time.
For example, exit strategies at recent Navy air
sparging sites in Southern California have included
provisions to transition to monitored natural attenuation
after reaching asymptotic removal of contaminants
based on results from quarterly groundwater
monitoring. At one site, system shutdown was granted
after greater than 80% mass removal of BTEX and
MTBE was achieved and asymptotic removal had
been reached (NFESC, 2000b). Shutdown was granted
even though cleanup goals for benzene and MTBE had
not been achieved in all monitoring locations.
Furthermore, the recommendation for system
shutdown was supported by the 100-fold increase in
monthly treatment costs per pound of contaminant
removed.
6.2 Long-Term Monitoring
After active remediation, a rational strategy for
reducing the coverage and frequency of groundwater
monitoring should be included in a site closure plan.
The objectives of long-term monitoring should be to
confirm that the groundwater plume is shrinking or remains stable, that natural processes continue to reduce
concentrations over the long term (seasonal variations
should be considered as having much less interpretive
value than consistent interseason trends), and that site
closure objectives will be achieved within a time
frame that will maintain protection of human health
and the environment. There are several good guidance
documents regarding long-term monitoring strategies
including NFESC’s Guide to Optimal Groundwater
Monitoring (2000a).
A suggested approach for reducing the cost of the
overall long-term monitoring program is to establish
decision criteria or project milestones that, when
achieved, will cause another phase of the monitoring
plan to begin. Each successive phase will consist of
less frequent monitoring of fewer wells. As uncertainty regarding the long-term behavior of the plume is
reduced, the need for monitoring is correspondingly
reduced. The reduction in monitoring should accompany reduced uncertainties in the spatial and temporal
behavior of the plume. In addition, monitoring plans
initially cover a broad range of constituents typically
due to uncertainties and complexities in thoroughly
describing the source of the plume. As knowledge is
gained by periodic monitoring, compounds can be
safely and responsibly dropped from the list.
41
Decision criteria for executing these changes to
the monitoring plan should be clearly described and
approved by regulatory authorities. Monitoring data
should not be collected, tabulated, plotted, and documented without further action. The objective of monitoring data is to aid in the management of the project
and the risk associated with the groundwater contaminants; therefore, data analysis should support a
management decision. For example, the monitoring
plan may include a requirement to review data gaps
and monitoring needs annually, with the agreement
that additional data will be collected only to meet
defined objectives.
6.3 Site Closure
Finally, project management should petition for
site closure when monitoring objectives are achieved,
plume concentrations have been reduced to cleanup
objectives, or concentrations are consistently decreasing
toward cleanup objectives. With appropriate interaction,
regulatory authorities should expect the petition for site
closure.
42
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Muehlberger, E.W., P. Hicks, and K. Harris. 1997. “Biosparging of a Dissolved Petroleum Hydrocarbon Plume.”
In: B.C. Alleman and A. Leeson (Eds.), In Situ and On
Site Bioremediation: Volume 1. Proceedings of the
Fourth International In Situ and On-Site Bioremediation
Symposium, New Orleans, April 28-May 1. Vol. 4(1):
209-210.
Kershner, M.A., and D.R. Theoret. 1997. “Horizontal Air
Sparging Utilized as A Site Control Measure.” In: B.C.
Alleman and A. Leeson (Eds.), In Situ and On Site
Bioremediation: Volume 1. Proceedings of the Fourth
International In Situ and On-Site Bioremediation Symposium, New Orleans, April 28-May 1. Vol. 4(1): 215-220.
Naval Facilities Engineering Service Center. 2000a. Interim
Final Guide to Optimal Groundwater Monitoring. Prepared by Radian International, White Rock, NM. January.
Available at: http://enviro.nfesc.navy.mil/erb/erb_a/
support/wrk_grp/raoltm/case_studies/Int_Final_Guide. pdf.
Kirtland, B.C. and C.M. Aelion. 2000. “Petroleum Mass
Removal from Low Permeability Sediment Using Air
Sparging/Soil Vapor Extraction: Impact of Continuous or
Pulsed Operation.” Journal of Contaminant Hydrology,
41: 367-383.
Naval Facilities Engineering Service Center. 2000b. Installation Restoration Program MTBE Cleanup Review Tiger
Team. SP-2096-ENV. December.
Klemm, D.E., S. Lummus, and S. Eaton. 1997. “Air Sparging
in Various Lithologies: 3 Case Studies.” In: B.C.
Alleman and A. Leeson (Eds.), In Situ and On Site
Bioremediation: Volume 1. Proceedings of the Fourth
International In Situ and On-Site Bioremediation Symposium, New Orleans, April 28-May 1. Vol. 4(1): 193-198.
NFESC, see Naval Facilities Engineering Service Center.
Roth, R.J., M. Kirshner, H.Y. Chen, and B. Frumer. 1998.
“Horizontal Air Sparging and Soil Vapor Extraction
Wells Remediating Jet Fuel in Soil and Groundwater at
JFK International Airport, New York.” In: P. Rominder,
S. Suri, and G.L. Christensen (Eds.), Hazardous and Industrial Wastes. Proceedings of the Hazardous and Industrial Wastes: 30th Mid-Atlantic Conference, Villanova
University, Villanova, PA, July 12-15.
Kram, M. 2001. “Performance Comparison: Direct-Push
Wells Versus Drilled Wells.” NFESC Technical Report
TR-2120-ENV. NFESC, Washington, DC.
Kraus, J., S. Nelson, P. Boersma, and A. Maciey. 1997.
“Comparison of Pre-/Post-Sparging VOC Concentrations
in Soil and Groundwater.” In: B.C. Alleman and A.
Leeson (Eds.), In Situ and On Site Bioremediation:
Volume 1. Proceedings of the Fourth International In Situ
and On-Site Bioremediation Symposium, New Orleans,
April 28-May 1. Vol. 4(1): 123-128.
Rutherford, K. and P.C. Johnson. 1996. “Effects of Process
Control Changes on Aquifer Oxygenation Rates During
44
In Situ Air Sparging in Homogeneous Aquifers.” Ground
Water Monitoring and Remediation, 16(4): 132-141.
U.S. EPA, see United States Environmental Protection
Agency.
Strzempka, C.P., P.E. Woodhull, T.M. Vassar, and D.E.
Jerger. 1997. “In-Situ Biosparging and Soil Vapor
Extraction for JP-4 Contaminated Soils and Groundwater: A Case Study.” Proceedings from The First International Conference on Remediation of Chlorinated and
Recalcitrant Compounds. Monterey, CA, May 18-21.
Physical, Chemical, and Thermal Technologies: Remediation of Chlorinated and Recalcitrant Compounds. pp.
245-250.
Vroblesky, D.A., and T.R. Campbell. 2000. “Simple, Inexpensive Diffusion Samplers for Monitoring VOCs in
Ground Water.” In: G.B. Wickramanayake, A.R.
Gavaskar, M.E. Kelley, and K.W. Nehring (Eds.), Risk
Regulatory, and Monitoring Considerations: Remediation of Chlorinated and Recalcitrant Compounds.
Proceedings of the Second International Conference on
Remediation of Chlorinated and Recalcitrant Compounds, Monterey, CA, May 22-25. Vol. C2-1: 349-356.
United States Army Corps of Engineers. 1995. Engineering
and Design–Soil Vapor Extraction and Bioventing. EM
1110-1-4001. November.
Wade, A., G.W. Wallace, S.F. Siegwald, W.A. Lee, and K.C.
McKinney. 1996. “Performance Comparison Between a
Horizontal and a Vertical Air Sparging Well: A FullScale One-Year Pilot Study.” Proc. National Outdoor
Action Conference Expo., 10th. pp. 189-206.
United States Army Corps of Engineers. 1998. Engineering
and Design–Monitoring Well Design, Installation, and
Documentation at Hazardous Toxic, and Radioactive
Waste Sites. EM 1110-1-4000. November.
Wiedemeier, T.H., J.T. Wilson, D.H. Kampbell, R.N. Miller,
and J.E. Hansen. 1995. “Technical Protocol for Implementing Intrinsic Remediation with Long-Term Monitoring for Natural Attenuation of Fuel Contamination
Dissolved in Groundwater.” Prepared for the U.S. Air
Force Center for Environmental Excellence, San
Antonio, TX.
United States Environmental Protection Agency. 1992. A
Technology Assessment of Soil Vapor Extraction and Air
Sparging. Prepared by U.S. EPA Office of Research and
Development. Washington, DC. EPA/600/R-92/173.
September.
USACE, see United States Army Corps of Engineers.
45
APPENDIX A
FOCUSED LITERATURE REVIEW
A literature review was performed to analyze the
lessons learned from recent field-scale air sparging remediation projects and to highlight improvements in conventional techniques for design, operation, and monitoring of in situ air sparging systems. This review does
not focus on the results of laboratory or modeling
research efforts. For a more complete summary of recent
advances in air sparging research, the literature review
by Johnson et al. (2001) should be consulted. The issues
covered in this review should help remedial project
managers anticipate and correct common performance
problems and improve the rate of success for implementation of air sparging remediation projects.
many as 134 injection wells. Table A-1 presents some
pertinent data from several selected sites. This table
should provide the reader with an idea of the scope and
size of some recent air sparging projects. The reader is
referred to Bass et al. (2000) for a detailed review of a
database of 49 air-sparging projects completed by a
single environmental consulting firm for both chlorinated
solvent and petroleum hydrocarbon contaminated sites.
Mass recovery rates drop off dramatically over the
lifetime of the air sparging project. For example, during
the Glass (2000) project, volatile organic compound
(VOC) mass recovery rates dropped by a factor of 20
over an eight-month period. In general, pilot study
results yield mass removal rates much higher than those
experienced during full system operation and therefore
provide limited information for the prediction of mass
recovery rates over the lifetime of a project. A DOE
(1995) pilot test of horizontal air sparging found that
soil vapor extraction (SVE) alone removed an estimated
109 lb/day, while the use of air sparging enhanced
removal by an additional 20 lb/day. This suggests that
under some circumstances VOC recovery from the
residual contamination in the vadose zone may be significantly greater than recovery induced by air sparging
at the water table. Remedial project managers should
A.1 Site Background Review
All of the field-scale air sparging projects reviewed
involved the cleanup of groundwater impacted by chlorinated solvents and/or petroleum hydrocarbons. Of the
articles chosen for review, eight dealt with chlorinated
solvents, ten dealt with petroleum hydrocarbons, and
two dealt with both types of compounds. The case
studies involved a variety of soil and aquifer conditions
and a variety of air sparging systems, from pilot studies
with one sparging well to full-scale systems with as
TABLE A-1. Summary of Site Parameters for Selected Air Sparging Remediation Projects
Compound(s)
DCA, DCE,
TCE, VC
DCE, PCE,
TCE, VC
DCE, PCE,
TCA, TCE,
methylene
chloride
TCA, TCE,
PCE
BTEX
BTEX
Description
of Geologic
Material
Fine-grained
sand
Sandy gravel
Medium to
coarse sand
and gravelly
sand
Sand with thin
lenses of clay
Silty sands
Sandy clay to
sandy clay loam
Depth to
Groundwater
6 ft bgs
Project
Size
Not listed
Duration
of
Operation
8 months
VOC Mass
Removal
Rate
22 to
1 lb/day
0.35 to
0.13 lb/day
12 to
2.4 lb/day
Number of
Sparge
Wells
3
134
Air
Flowrate
per Well
10 to
15 cfm
30 to
110 cfm
Not listed
15 to 25 ft
bgs
0.5 to 9 ft
bgs
Not listed
1 year
1.7 acres
450 days
120 ft bgs
1 acre
139 days
72 hours
140 to
100 lb/day
0.06 lb/day
1
(horizontal)
1
65 to
270 cfm
1 to 3 cfm
20 ft bgs
3,000 ft
2
20 to 25 ft
bgs
1,200 ft
2
44 days
32 lb/day
6
A-1
5
Reference
Glass, 2000
USACE,
1998
Gordon, 1998
DOE, 1995
Murray et al.,
2000
0.5 to 5 cfm Kirtland and
Aelion, 2000
systems. The following discussion contains suggestions
on improving the design of conventional air sparging
systems, as well as suggestions for the implementation
of innovative air sparging projects at sites with less than
optimal geologic characteristics.
consider the initial contaminant distribution and the
remedial action goals in deciding when the extra cost of
installing an air sparging system is warranted.
Bass et al. (2000) found that almost half of the air
sparging sites reviewed in their study achieved a 95%
average permanent reduction in groundwater VOC concentrations. The percent reductions in groundwater VOC
concentrations ranged from 27% to almost 100% for all
49 sites reviewed. However, at several of these sites,
permanent reductions in groundwater VOC concentrations greater than 90% were still insufficient to meet
stringent cleanup standards. Table A-2 shows a sample
of percent reductions in target compounds from several
selected sites, along with a comparison to the respective
remedial action objectives. A number of sites did not
achieve closure levels despite high mass removal via air
sparging. It is clear that remedial project managers need
to develop a long-term closure strategy for each site
because air sparging alone may not achieve cleanup
standards. One possibility is the use of a site-specific
risk assessment to negotiate with local or state regulators to set more appropriate and feasible remediation
goals. Another possibility is to transition to monitored
natural attenuation once the air sparging system reaches
asymptotic levels of VOC recovery.
q The study by Bass et al. (2000) showed that the
most successful air sparging systems consisted of
those with wells spaced an average of 28.6 ft
apart. For petroleum sites where a smear zone is
present, Bass et al. suggest a more aggressive
approach to sparge well spacing of 15 to 20 ft or
an assumed radius of influence of 7 to 10 ft.
q Although most studies involved spatially varied
monitoring points and monitoring wells, at least
one (Murray et al., 2000) had vapor monitoring
points that were lined up along one axis because of
site access problems. Vapor monitoring points
should be spatially varied and placed at several
different angles from the sparge well because preferential flow and channeling make the air distribution pattern unpredictable. A straight line of
monitoring points might provide inadequate or
nonrepresentative data (Bruce et al., 2001).
q Several of the full-scale project sites reviewed
contained networks of wells ranging 3 to 134 wells
(Glass, 2000, Gordon et al., 1998, Hartley et al.,
1999, Klemm et al., 1997, Kraus et al., 1997,
Maheux and McKee, 1997). The full-scale system
A.2 Design Issues Review
Several issues were addressed in the literature
regarding the successful design of full-scale air sparging
TABLE A-2. Example Percent Contaminant Reductions after Air Sparging Application
at Selected Sites
Percent
Reduction for
Each
Contaminant
DCE 100%
TCE 92%
VC 100%
DCE 9%
PCE 82%
TCE 95%
TCE 99.9%
Duration
Initial Groundwater Final Groundwater Remedial Action
of
Compound(s)
Concentrations
Concentrations
Objective
Operation
DCE, PCE,
DCE at ND
12 months
DCE at 7 mg/L
TCE < 5 mg/L
TCE, VC
TCE at 6.4 mg/L
TCE at 79 mg/L
VC < 1 mg/L
VC at ND
VC at 7.8 mg/L
DCE, PCE,
9 months
DCE at 26,400 mg/L DCE at 24,000 mg/L
PCE < 5 mg/L
TCE
PCE at 6,670 mg/L
PCE at 1,200 mg/L
TCE < 5 mg/L
TCE at 9,870 mg/L
TCE at <500 mg/L
DCA, DCE,
8 months
TCE at 978,000 mg/L
TCE at 845 mg/L
TCE <1,000 mg/L
TCE, VC
BTEX
BTEX at
BTEX 99.9%
15 months
BTEX at 1 mg/L
BTEX < 2 mg/L
15,000 mg/L
Ethylbenzene
E 98%
10 months
E at 20,000 mg/L
E at 410 mg/L
E < 680 mg/L
(a)
and xylenes
X 99%
X at 100,000 mg/L
X at 660 mg/L
X <1,750 mg/L
(a) Remedial action objectives not provided for this site, so drinking water MCLs were added for comparison.
ND = not detected.
A-2
Reference
USACE, 1998
Hughes and
Dacyk, 1998
Glass, 2000
Hartley et al.,
1999
Kraus et al.,
1997
should be designed to allow flexibility in delivering airflow to individual wells and groups of
wells. The sparging wells should be clustered in
groups of two to five wells and each well should
have its own pressure regulator and airflow meter
to ensure that adequate airflow distribution is
occurring within the network of wells (Johnson et
al., 2001).
observed to be below the biodegradation capacity
of the vadose zone, in situ biodegradation may be
a viable alternative for vapor management. This
situation would be equivalent to an aggressively
designed and operated biosparging application. A
brief review of the literature shows that initial
concentrations at biosparging sites ranged from
0.69 mg/L to the presence of free product (see
Table A-3). None of the selected projects
employed soil vapor extraction; however, one
system (Klemm et al., 1997) used biorespiration
monitoring to track contaminant biodegradation
rates and estimate hydrocarbon emissions to the
surface.
q The Bass et al. study noted that air sparging is
generally more efficient at high flowrates typically
ranging from 6 to 20 cfm.
q When selecting air sparging as an option for site
remediation, there are generally two modes of
technology application based on the primary
removal mechanism that the design objective
maximizes.
TABLE A-3. Initial Contaminant Concentrations
for Selected Sites where Biosparging is
the Stated Remediation Objective
1. Biosparging, which involves the injection of air
into the subsurface to promote aerobic
biodegradation of the contaminant, and
2. Air sparging, which relies on the partitioning of
volatile organic compounds from the dissolved
or free phase to the vapor phase (air stripping).
Compound(s)
VC
BTEX
BTEX
BTEX
TPH, BTEX
q Through the development of a simplified conceptual model, Johnson (1998) noted that if aerobic
biodegradation occurs at a site, it will only
enhance air sparging performance at initial VOC
concentrations less than 1 mg/L in groundwater.
At contaminant concentrations greater than
1 mg/L, the volatilization process will be the dominant driving force for mass removal from groundwater. Stripped vapors that reach the vadose zone
can then be biodegraded if adequate oxygen is
present in the vapor stream. For aerobically
biodegradable contaminants, the biodegradation
capacity of the vadose zone can be determined by
performing site-specific tests in which the injection flowrate is increased until acceptable atmospheric emissions are observed, at which point the
biodegradation capacity of the vadose zone has
been exceeded. These tests should be performed
by experienced practitioners. When volatile contaminant concentrations are significantly greater
than 1 mg/L at a site and the site geology allows
high injection flowrates, air sparging should be
considered the preferred application and steps
should be taken to manage and monitor soil vapor
migration. If the air sparging injection rate is
Initial
Groundwater
Concentration
0.69 mg/L
0.157 to
11 mg/L
10 to 20 mg/L
15 mg/L
Free product
Reference
Cannata et al., 2000
Muehlberger et al.,
1997
Payne et al., 1997
Hartley et al., 1999
Klemm et al., 1997
q Although air sparging is a widely used technology,
several common conditions at sites can impede
successful implementation. According to Sittler
and Peacock (1997), less than 25% of remediation
sites nationwide are amenable to conventional air
sparging due to variable geologic and hydrogeologic conditions. However, the literature review
suggests that air sparging may still be a viable
option at sites with low permeability formations
and at sites with high water tables.
q According to Kirtland and Aelion (2000), it is
widely accepted that air sparging and soil vapor
extraction is best suited to homogenous, sandy
formations with hydraulic conductivities on the
order of 10-3 cm/s. Kirtland and Aelion suggest,
however, that low flowrates and pulsing might still
be effective for the implementation of air sparing
at low permeability sites. At a site with hydraulic
conductivities ranging from 6 × 10-7 to 3 × 10-4,
A-3
10 pulsed air sparging tests removed approximately 78 kg of petroleum hydrocarbons over a
23-day period. For the remediation of chlorinated
solvents in low permeability soils, Marley (1996)
suggests that the best technologies are modifications to in situ air sparging including recirculatory
sparging systems, sparging/biosparging trenches,
and induced fracturing techniques.
the path of least resistance moving preferentially
through areas with gaps in coverage. During the
monitoring phase of the project, however, it was
determined that the areal extent of the sparging
zone was approximately half as wide at the far end
compared to the near end of the horizontal well
during low flow conditions. At high flow conditions (320 scfm at 11 psi), the areal extent of the
sparge zone was more uniform.
q Air sparging projects should generally not be
implemented in areas with high water tables
(depth to groundwater < 5 ft bgs) because the use
of soil vapor extraction wells will be impractical.
If necessary, some innovative modifications such
as horizontal SVE wells, horizontal SVE trenches,
or multiphase vapor-liquid pumps may be useful
in effecting soil vapor control at these sites
(Gordon, 1998).
A.3 Operational Issues Review
Several system performance problems can be
overcome by changing the operation of the air sparging
system from a continuous mode to cycling and/or pulsing of air injection. Several articles recommend the use
of cycling and pulsing over the use of continuous air
injection (Gordon, 1998; Johnson et al., 2001; and
Kirtland and Aelion, 2000). For this discussion, cycling
is defined as turning the system on/off over a period of
weeks or months, while pulsing is defined as turning the
system on/off over a period of hours.
q The use of horizontal wells in environmental projects is increasing because of recent innovations in
drilling techniques and declining installation costs.
By 1995, the Department of Energy had documented the installation of over 100 horizontal
environmental wells, with 25% for groundwater
extraction, 25% for soil vapor extraction, and 50%
for other purposes including air injection, bioventing, and petroleum recovery (DOE, 1995).
Several articles are available for review regarding
the use of horizontal wells in air sparging projects
(DOE, 1995; Kershner and Theoret, 1997; Roth et
al., 1998; and Wade et al., 1996). Roth et al.
(1998) discusses a case study at an airport in New
York where 27 horizontal air sparging wells and
15 horizontal soil vapor extraction wells were used
to clean up a jet fuel spill. The air sparging wells
were 680 ft in length and installed at a depth of
12 ft bgs, while the soil vapor extraction wells
were 660 ft in length and installed at a depth of 3.5
to 5 ft bgs. The system removed approximately
47,000 lb of VOCs over an 18-month period of
operation. Horizontal wells were the preferred
technology at this site because of the large area of
coverage needed and the restricted access to the
runways and terminal area. Wade et al. (1996)
discusses the use of a 200-ft horizontal well as a
barrier to the migration of a chlorinated solvent
plume. Horizontal technology was selected
initially because it was believed that a line of
vertical sparge wells would not create a uniform
curtain of air and that groundwater would follow
q Although pulsing is widely encouraged, Bass et al.
(2000) has found that continuous mode systems
can still be effective. The fact that continuous
mode systems represented 61% of the most
successful air sparging projects in their review
suggests that continuous mode systems are still
viable. Bass et al. (2000), however, states that
pulsing does improve sparging performance by
increasing mixing and the sparged zone of influence. Pulsing also has economic benefits because
it allows for a reduction in the size of the compressor needed to run a network of sparge wells and
also decreases energy usage. Case studies from
petroleum hydrocarbon sites suggest that a 20% to
30% increase in mass removal rates can be
achieved by pulsing the injected air (Bruce et al.,
2001; Kirtland and Aelion, 2000). Kirtland and
Aelion demonstrated that in a low permeability
formation, BTEX and TPH mass removal rates
increased from 14.3 kg/day under continuous
operation to 17.6 kg/day under 8-hour pulsing of
air injections.
q Based on the Bass et al. (2000) database, the projects that implemented pulsing had pulse times
ranging from 0.5 to 24 hours, with an average
pulse time of 10 hours. Only limited guidance is
A-4
available in the literature on how to select the
pulse time. It has been suggested in the literature
that pulse times be determined via the time
required for hydraulic gradients (local groundwater mounding) to dissipate after the onset or
termination of an interval of air sparging (Wade et
al., 1996).
groundwater VOC concentrations. Rebound is
particularly prevalent at petroleum hydrocarbon
sites where a light NAPL smear zone is present
and the seasonal fluctuation of the water table
exposes the groundwater to new sources of contamination (Bass et al., 2000). Cycling can also
allow substantial savings in vapor treatment costs.
After a temporary system shutdown on the order
of weeks or months, the higher VOC vapor concentrations may require less supplemental fuel to
combust in a thermal or catalytic oxidizer.
q For source zone air sparging wells, pulsing over
periods of hours can minimize the effects of
hydraulic mounding and contaminant migration.
Hydraulic mounding can be mitigated by setting
up a network of sparge wells, and sparging the
downgradient wells first (Gordon, 1998).
q Testing of startup modes for air sparging systems
has indicated that a gradual system startup is better
than a sudden burst of flow. The subsurface
appears to exhibit a “memory” of the air channel
structures between pulses, and the initial formation
of the channel structure is important for future
operations (Gordon, 1998).
q Frequently, after the startup of a sparging system
in the source zone, residual product will be liberated and may temporarily increase groundwater
concentrations in the vicinity of the sparge well.
Any free product identified should be removed by
hand bailing or other methods (Gordon, 1998).
A.4 Monitoring Issues Review
q For downgradient air sparging wells, used as a
contaminant migration barrier, the system operator
should avoid increasing the air saturation to the
point that a reduction in hydraulic conductivity
causes bypassing of groundwater around the well
network. Again, pulsing at the proper time intervals can minimize this effect (Gordon, 1998).
At most field sites, monitoring efforts are minimized to weekly or monthly system checks. During
operation of an air sparging system, several parameters
are monitored including in situ soil vapor concentrations, SVE off-gas concentrations, dissolved oxygen
levels, and water level measurements. Most air sparging
projects also require initial baseline and final site characterization studies, which include soil and groundwater
sampling efforts. Several new techniques for system
monitoring and site characterization have been suggested by Johnson et al. (2001) to improve air sparging
system performance at larger, more complicated sites
which demand a site-specific approach.
q As air sparging in the subsurface continues, VOC
recovery will drop off dramatically over time
because the most readily available contaminants
volatilize first. As shown in Glass (2000), VOC
mass recovery rates dropped by a factor of 20 after
eight months of air sparging operation. At this
point, the VOC mass recovery rate becomes
limited by the rate of diffusion from the residual or
free product to the groundwater. Cycling over a
period of weeks allows for the slow process of diffusion-limited mass transfer to take place during
extended system shutdowns. Projects that implement cycling will also have less of a rebound
effect six months to a year after the end of active
operation (Gordon, 1998). Poor performance at
sparging sites can often be attributed to a rebound
in VOC concentrations after the system has been
shut down. Bass et al. (2000) found that rebound
at the least successful sites averaged 0.68 or two
orders of magnitude of rebound for every three
orders of magnitude of initial reduction in
q In order to better characterize a site, it is suggested
that one continuous core from the top of the injection well screen to the water table be obtained and
photographed for future reference at or near each
sparge well location.
q Johnson suggests the use of helium (He) and sulfur
hexafluoride (SF6) tracer studies to enhance understanding of the sparging zone of influence. The
distribution of the helium or SF6 in vapor monitoring points provides an idea of the location of
preferential paths and/or channels and allows a
quantitative assessment of the air distribution
pattern around the sparge well. This data can be
A-5
used to identify treatment dead zones and help in
planning modifications to the number of sparge
wells or the flowrate of the sparge wells in a large
network. Tracer tests can also be used to estimate
the capture efficiency of the soil vapor extraction
system.
Biodegradation during In Situ Air Sparging. Submitted to
Bioremediation Journal.
Bass, D.H., N.A. Hastings, and R.A. Brown. 2000. Performance of Air Sparging Systems: A Review of Case
Studies. Journal of Hazardous Materials, (72)101-119.
Bruce, C.L., P.C. Johnson, R.L. Johnson, and A. Leeson.
2001. Assessment of the In Situ Air Sparging Design
Paradigm at a Gasoline-Spill Site. Submitted to Bioremediation Journal.
q The use of transient water-level pressure transducers in nearby groundwater monitoring wells is
recommended for pilot test activities. The pressure transducers provide data that indicate the
effect of air sparging on water table mounding and
on the time it takes for the air injected into the
subsurface to find an outlet or vent to the vadose
zone. For aquifers with silt and clay lenses or
stratified layers, the pressure may continue to
build for hours or days before a release occurs.
This data can be used to determine if a site is
suitable for air sparging, and it can also be used to
estimate appropriate shutdown times for pulsed
operation (Johnson et al., 2001).
Cannata, M.A., S.W. Hoxworth, T.P. Swingle, and E. Carver.
2000. Pilot Testing and Implementation of Biosparging
for Vinyl Chloride Treatment. Proceedings from The
Second International Conference on Remediation of
Chlorinated and Recalcitrant Compounds. Monterey, CA,
May 22-25. Physical and Thermal Technologies: Remediation of Chlorinated and Recalcitrant Compounds. pp.
9-18.
DOE, see U.S. Department of Energy.
Glass, S.A. 2000. Deep Air Sparging of a Chlorinated Solvent
Source Area. Proceedings from The Second International
Conference on Remediation of Chlorinated and Recalcitrant Compounds. Monterey, CA, May 22-25. Physical
and Thermal Technologies: Remediation of Chlorinated
and Recalcitrant Compounds. pp. 75-81.
q The use of multitracer push-pull tests is recommended during the pilot test phase. The data from
these tests can be used to calculate the volatilization rates and oxygen utilization rates in the subsurface. The reader should consult Amerson-Treat
et al. (2001) for more information on this type of
performance test.
Gordon, M.J. 1998. Case History of a Large-Scale Air
Sparging/Soil Vapor Extraction System for Remediation
of Chlorinated Volatile Organic Compounds in Ground
Water. Ground Water Monitoring and Remediation.
(18)137-149.
Hartley, J.D., L.J. Furlow, and W.N. Zwiren. 1999. Cycled
Air Sparging: Field Results in a High-Velocity Aquifer.
Proceeding from the Fifth International In Situ and OnSite Bioremediation Symposium. San Diego, CA, April
19-22. In Situ Bioremediation of Petroleum Hydrocarbon
and Other Organic Compounds. pp. 77-81.
q Wardwell (1999) describes the use of groundwater
velocity probes (manufactured by HydroTechnics,
Inc.) at a petroleum hydrocarbon, air sparging
remediation project in Port Hueneme, California.
These sensors allowed in situ measurement of
three-dimensional groundwater flow. The study
indicated that the effects of groundwater mounding dissipated within 24 hours of the start of air
sparging at the site and that hydraulic mounding
likely had little impact on the distribution or
spreading of hydrocarbon contaminants. The
study also indicated that at airflow injection rates
greater than 10 cfm, the groundwater flow direction was diverted away from the sparge area.
Hughes, W.D., and P.I. Dacyk. 1998. Air Sparging of Chlorinated Volatile Organic Compounds in a Layered Geologic Setting. Proceedings from The First International
Conference on Remediation of Chlorinated and Recalcitrant Compounds. Monterey, CA, May 18-21. Physical,
Chemical, and Thermal Technologies: Remediation of
Chlorinated and Recalcitrant Compounds. pp. 279-284.
Johnson, P.C. 1998. Assessment of the Contributions of Volatilization and Biodegradation to In Situ Air Sparging
Performance. Environ. Sci. Technol. (32)276-281.
A.5 References
Johnson, P.C., R.L. Johnson, C.L. Bruce, and A. Leeson.
2001. Advances in In Situ Air Sparging/Biosparging.
Submitted to Bioremediation Journal.
Amerson-Treat, I.L., C.L. Bruce, P.C. Johnson, and R.L.
Johnson. 2001. A Multi-Tracer Push-Pull Diagnostic Test
for Assessing the Contributions of Volatilization and
Kershner, M.A., and D.R. Theoret. 1997. Horizontal Air
Sparging Utilized as a Site Control Measure. Proceedings
A-6
Station Cecil Field, Jacksonville, Florida. Journal of
Hazardous Materials. (72)121-145.
from the Fourth International In Situ and On-Site
Bioremediation Symposium. New Orleans, April 28-May
1. In Situ and On Site Bioremediation: Volume 1. pp.
215-220.
Payne, E., M. Gallagher, S. Pinizzotto, and E. Nobles-Harris.
1997. Air Sparging Below Hydrocarbon Free Product
Without Vapor Control. Proceedings from the Fourth
International In Situ and On-Site Bioremediation Symposium. New Orleans, April 28-May 1. In Situ and On Site
Bioremediation: Volume 1. pp. 181-186.
Kirtland, B.C., and C.M. Aelion. 2000. Petroleum Mass
Removal from Low Permeability Sediment Using Air
Sparging/Soil Vapor Extraction: Impact of Continuous or
Pulsed Operation. Journal of Contaminant Hydrology,
(41)367-383.
Roth, R.J., M. Kirshner, H.Y. Chen, and B. Frumer. 1998.
Horizontal Air Sparging and Soil Vapor Extraction Wells
Remediating Jet Fuel in Soil and Groundwater at JFK
International Airport, New York. 30th Mid-Atlantic
Industrial and Hazardous Waste Conf.
Klemm, D.E., S. Lummus, and S. Eaton. 1997. Air Sparging
in Various Lithologies: 3 Case Studies. Proceedings from
the Fourth International In Situ and On-Site Bioremediation Symposium. New Orleans, April 28-May 1. In
Situ and On Site Bioremediation: Volume 1. pp. 193-198.
Sittler, S.P., and M.P. Peacock. 1997. Innovative Air Sparging Modifications to Remediate Organic Compounds in
Non-Optimum Geologic Formations. Proceedings of the
11th National Outdoor Action Conf. Expo. pp 259-271.
Kraus, J., S. Nelson, P. Boersma, and A. Maciey. 1997. Comparison of Pre-/Post-Sparging VOC Concentrations in
Soil and Groundwater. Proceedings from the Fourth
International In Situ and On-Site Bioremediation Symposium. New Orleans, April 28-May 1. In Situ and On-Site
Bioremediation: Volume 1. pp. 128-128.
U.S. Army Corps of Engineers. 1998. Air Sparging and Soil
Vapor Extraction at Landfill 4, Ft. Lewis Washington.
Cost and Performance Report. September.
Maheux, P.J., and R.C.E. McKee. 1997. An In Situ Air Sparging Method: Contiguous Belled Sand Columns. Proceedings from the Fourth International In Situ and On-Site
Bioremediation Symposium. New Orleans, April 28May 1. In Situ and On Site Bioremediation: Volume 1.
pp. 221-226.
U.S. Department of Energy. 1995. In Situ Air Stripping Using
Horizontal Wells: Innovative Technology Summary
Report. Report No.:DOE/EM-0269; NTIS Number:
DE96003564. Prepared by Stone and Webster Environmental Technology and Services, Boston, MA. April.
p. 31.
Marley, M.C. 1996. Air Sparging in Low Permeability Soils.
Remediation of DNAPL in Low Permeability Media
Project. pp. 8-1–8-19.
Wade, A., G.W. Wallace, S.F. Siegwald, W.A. Lee, and K.C.
McKinney. 1996. Performance Comparison Between a
Horizontal and a Vertical Air Sparging Well: A FullScale One-Year Pilot Study. Proc. National Outdoor
Action Conference Expo., 10th. pp. 189-206.
Muehlberger, E.W., P. Hicks, and K. Harris. 1997. Biosparging of a Dissolved Petroleum Hydrocarbon Plume.
Proceedings from the Fourth International In Situ and
On-Site Bioremediation Symposium. New Orleans, April
28-May 1. In Situ and On Site Bioremediation: Volume 1.
p. 209.
Wardwell, D.A. 1999. Groundwater Flow Sensor Monitoring
of Air Sparging. Proceeding from the Fifth International
In Situ and On-Site Bioremediation Symposium. San
Diego, CA, April 19-22. In Situ Bioremediation of Petroleum Hydrocarbon and Other Organic Compounds. pp.
47-57.
Murray, W.A., R.C. Lunardini Jr., F.J. Ullo Jr., M.E.
Davidson. 2000. Site 5 Air Sparging Pilot Test, Naval Air
A-7
APPENDIX B
COMPENDIUM OF COMPETING REMEDIAL TECHNOLOGIES
This appendix describes the remedial technologies that may be competitive with the application of in situ air sparging
for groundwater remediation. The various technologies are as follows:
Pump and Treat
In Situ Chemical Oxidation
Enhanced In Situ Aerobic Bioremediation
In-Well Air Stripping/Groundwater Circulating Wells
Monitored Natural Attenuation
Phytoremediation
Reactive Barriers
Surfactant-Enhanced Aquifer Remediation
In Situ Thermal Treatment
Two-Phase (Dual-Phase) Extraction
B-1
SUMMARY SHEET
Air Sparging vs. Pump and Treat
air sparging because groundwater extraction well positions
and flowrates needed to capture the plume typically can be
determined accurately with groundwater modeling methods.
Technology Description – Pump and Treat
Pump and treat consists of one or more wells from which
contaminated groundwater is pumped to the surface for
treatment. The aboveground treatment system consists of a
sequence of physical, chemical, or biological units designed
to perform operations such as phase separation, precipitation, and activated sludge treatment. After treatment, the
groundwater commonly is discharged to a sewage treatment plant. Site-specific conditions may allow discharge
to local surface water or reinjection of treated groundwater. Figure 1 shows a conceptual diagram of a pump
and treat system.
Water treatment required for a pump and treat system
typically is more complex than the off-gas treatment system that may be needed for the air sparging system.
Initial equipment costs for installation are low to moderate
(typically similar to that of an air sparging system), but the
materials and operating labor needed for the water treatment system results in higher operating costs for a pump
and treat system compared to an air sparging system.
The mass removal rate in the dissolved phase by a pump
and treat system is very low due to low solubility of organic
contaminants and slow release of sorbed contaminants. As
a result, the operating time typically is longer than that of
an air sparging system, resulting in higher project costs,
except when contaminants with very low sorption rates,
like MTBE, are considered.
For a well-defined plume, a pump and treat system can be
effective as a first line of defense in preventing further
migration and in removing the bulk of free product, but
typically is not cost-effective for remediation of an entire
plume.
Sources for Further Information
FIGURE 1. CONCEPTUAL DIAGRAM OF TYPICAL PUMP AND
TREAT SYSTEM
Powers, J.P. 1992. Construction Dewatering. John Wiley &
Sons, Inc., New York, NY.
Advantages and Limitations
Relative to Air Sparging
U.S. Environmental Protection Agency. 1996. A Citizen’s Guide
to In Situ Soil Flushing. EPA/542/F-96/006. Office of Solid
Waste and Emergency Response, Washington, DC.
The pump and treat approach is a mature technology with
well-established design standards and an established track
record. System design is more straightforward than with
B-2
SUMMARY SHEET
Air Sparging vs. In Situ Chemical Oxidation
Technology Description – In Situ
Chemical Oxidation
In situ chemical oxidation treatment involves injecting a
solution of oxidizing agent into groundwater to destroy dissolved contaminants. The technology is implemented by
drilling wells so that the oxidizing solution can be injected
into the contaminated zone. Hydrogen peroxide (H2O2),
hydrogen peroxide with ozone (H2O2/O3), Fenton’s Reagent
(iron-catalyzed hydrogen peroxide), and potassium permanganate (KMnO4) are the most commonly used oxidants
used for treating organic contaminants in groundwater.
Figure 1 shows a conceptual diagram of a chemical oxidation injection point.
FIGURE 1. CONCEPTUAL DIAGRAM OF CHEMICAL
OXIDATION INJECTION POINT
Advantages and Limitations
Relative to Air Sparging
In situ chemical oxidation is an innovative technology that
allows in situ destruction of contaminants. Chemical oxidation has a 50-year history of commercial-scale use for
ex situ water treatment to reduce organic pollutant concentrations, biological oxygen demand (BOD), chemical oxygen demand (COD), and/or odor and color, and currently
is being extended to in situ remediation of groundwater.
has the potential to displace the plume and increase chemical migration.
Injection of a chemical oxidation solution will be regulated under UIC regulations.
Sources for Further Information
Successful application of in situ chemical oxidation is
very sensitive to site conditions such as natural organic
matter content and hydrogeology. The range of applicable
sites for in situ chemical oxidation is more limited than for
air sparging. It may be difficult to achieve good mixing
between the groundwater and the oxidant solution. The
injected solution tends to displace the affected groundwater and then react with natural organic matter before it
reacts with affected groundwater. Oxidant solution injection
Edelstein, G. 1998. “Guidelines for Using Fenton’s Reagent at
Remedial Sites.” Underground Tank Technology Update,
12(4): 4-5. University of Wisconsin, Madison, WI.
Rahman, M., D.A. Schupp, E.R. Krishnan, A.N. Tafuri, and
C.T. Chen. 1999. “Pilot-Scale Evaluation of Chemical Oxidation of MTBE-Contaminated Soil.” In: Proceedings of
the 92nd Air and Waste Meeting and Exhibition. Air and
Waste Management Association, Pittsburgh, PA.
B-3
SUMMARY SHEET
Air Sparging vs. Other Oxygen Delivery Options
for Enhanced In Situ Aerobic Biodegradation
selection and system design. Table 1 lists achievable concentrations from various commercially available oxygen sources and
provides an order-of-magnitude estimate of the cost of oxygen
for each source.
Technology Description
In order to enhance in situ aerobic biodegradation, the limited
supply of oxygen in the subsurface should be overcome by an
engineered oxygen delivery system. This typically results in
enhanced aerobic biodegradation rates that are adequate for site
remediation. Although other limiting factors can exist, such as
the supply of nutrients, they typically are of secondary importance to oxygen levels.
TABLE 1. OXYGEN CONCENTRATION IN WATER ACHIEVED
BY VARIOUS SOURCES
Oxygen Source
Oxygen delivery systems may be either active or passive. Active
delivery, as used for air sparging, is the forced injection of
oxygen or air into the saturated zone. Pure oxygen sources can
be used, but have rarely been demonstrated to be economical.
Passive delivery is the introduction of oxygen in some form
such as solid peroxide, which is placed in the aquifer to aerate
groundwater as it flows under a natural gradient. Aquifer oxygenation with oxygen release compounds (ORCs) involves
placing ORC in porous bags in conventional drilled wells or by
injecting a slurry of ORC into push-well points. Liquid delivery
consists of dissolving oxygen into water and then using the
water as the carrier to deliver oxygen. In the case of hydrogen
peroxide (H2O2) the H2O2 is dissolved into water and oxygen is
produced by decomposition.
Achievable Oxygen
Concentration
Range, mg/L
Estimated Cost
of Oxygen,
$/Pound
Air
8 to 10
0.01
Pure Liquid
Oxygen (LOX)
40 to 50
0.1
Pure Oxygen
(generated)
40 to 50
1
Liquid H2O2
25 to 50
10
Solid Peroxide
25 to 50
100
In many applications the decision driver will be the cost of
oxygen because of the magnitude of typical oxygen demands.
At some sites other considerations are appropriate. For example,
the least expensive form of oxygen (air) has operation and maintenance costs associated with the equipment (compressors and
blowers) necessary to deliver the oxygen. The effectiveness of
oxygen distribution can be a very specific consideration, and is
typically a site- and case-specific consideration. At sites with
high oxygen demand such as petroleum hydrocarbon source
areas it may not be economically feasible to deliver sufficient
oxygen in a dissolved form no mater what the source.
Advantages and Limitations
Relative to Air Sparging
Active oxygen delivery options are primarily limited by the
solubility of oxygen in water, and are strongly influenced by
aquifer permeability and flow characteristics. Passive alternatives are limited by the diffusion rate of oxygen in water, and
distribution problems caused by heterogeneities in the aquifer
material. There are numerous other limitations to the various
oxygen delivery options which are specific to the approach. For
example, it has proven very difficult to control the rate of hydrogen peroxide decomposition when using H2O2, which has resulted
in poor oxygen distribution. During air sparging, consideration
must be given to the fate of the air injected and an off-gas
collection and treatment system may be required. Similarly, in
the case of solid peroxides, pH increase may become a problem.
These technology and site-specific limitations must be considered on a site and case specific basis.
Because of its low cost, air sparging is a commonly selected
alternative for remediating hydrocarbons in the saturated zone.
Solid peroxides such as Oxygen Release Compound (ORC®) are
widely used at sites with low operation and maintenance
requirements.
With reasonable estimates of oxygen demand at contaminated
sites ranging from thousands to (conceivably) millions of
pounds, the cost of oxygen becomes a critical factor in remedy
U.S. Environmental Protection Agency. 1996. A Citizen’s Guide
to Bioremediation. EPA/542/F-96/007. Office of Solid Waste
and Emergency Response, Washington, DC.
Sources for Further Information
Rawe, J., and E. Meagher-Hartzell. 1996. “In Situ Biodegradation Treatment.” In J.R. Boulding (Ed.), EPA Engineering
Sourcebook. Ann Arbor Press, Inc., Chelsea, MI. pp 143-163.
B-4
SUMMARY SHEET
Air Sparging vs. Nutrient Addition
for Enhanced In Situ Aerobic Bioremediation
Technology Description – Enhanced
In Situ Aerobic Bioremediation
Some inorganic contaminants may be immobilized by soil oxidation.
Enhanced in situ aerobic bioremediation processes often involve
the delivery of oxygen to the aquifer to stimulate natural biodegradation of contaminants in soil or groundwater and the
addition of other nutrients and/or cometabolites. A water solution of amendments usually is injected into upgradient wells or
trenches and circulated through the contaminated zone by removing groundwater from downgradient wells. This circulation of
the amendment solution through the contaminated zone provides
mixing and contact between the oxygen, nutrients, contaminants, added cometabolics, and microorganisms.
Achieving controlled flow and uniform oxygen delivery in the
aquifer can be difficult. Amendment solution flow must be controlled to avoid contaminant escape from zones of active biodegradation. Low-permeability soils are difficult to treat. Subsurface heterogeneity can make it difficult to deliver amendments
throughout the different zones of contamination, resulting in rapid
remediation in the higher permeable zones and insignificant to
slow remediation in the tighter zones where oxygen/ nutrient
diffusion rates limit effectiveness. Concentrations of hydrogen
peroxide greater than 100 to 200 mg/L in groundwater inhibit the
activity of microorganisms. Furthermore, rapid breakdown of
hydrogen peroxide by soil microbe enzymes and minerals can
limit its effectiveness. Iron precipitation and/or other changes in
groundwater chemistry can cause permeability reductions through
fouling and result in reduced ability to deliver amendments.
Some chlorinated organics (e.g., TCE, chlorobenzene, and PCBAroclor 1242) can be treated by cometabolic techniques that
involve adding a primary substrate to support the growth of the
microorganisms that fortuitously or coincidentally promote contaminant degradation. Figure 1 shows a conceptual diagram of a
typical enhanced aerobic bioremediation system.
The added oxygen can be consumed by biotic and abiotic
mechanisms near the injection well, which creates two significant problems: (1) biological growth can be limited to the region
near the injection well, limiting the treatment zone area and (2)
biofouling of wells can retard the input of recirculated groundwater or injected gases.
Most in situ bioremediation approaches use commercially available materials and conventional methods. As a result, the initial
capital cost to install the system is low to moderate (typically
similar to that of an air sparging system), but remediation is slow,
typically requiring several years to decades to reach cleanup
levels. The long operating time contributes to high monitoring,
operation and maintenance costs. Both biotic and abiotic sinks
for oxygen can prolong treatment duration, resulting in higher
operation, monitoring, and maintenance costs. As a result, the
operating time typically is longer than that of an air sparging
system, resulting in higher project costs.
Sources for Further Information
FIGURE 1. CONCEPTUAL DIAGRAM OF TYPICAL ENHANCED
AEROBIC BIOREMEDIATION SYSTEM
Rawe, J., and E. Meagher-Hartzell. 1996. “In Situ Biodegradation Treatment.” In J.R. Boulding (Ed.), EPA Engineering
Sourcebook. Ann Arbor Press, Inc., Chelsea, MI. pp 143-163.
Advantages and Limitations
Relative to Air Sparging
U.S. Environmental Protection Agency. 1996. A Citizen’s Guide
to Bioremediation. EPA/542/F-96/007. Office of Solid
Waste and Emergency Response, Washington, DC.
Enhanced in situ aerobic bioremediation is an innovative technology with a limited history of full-scale application. The technology promotes in situ removal or detoxification of contaminants
using natural low intensity biological transformation processes.
B-5
SUMMARY SHEET
Air Sparging vs. In-Well Air Stripping/Groundwater Circulating Wells
Technology Description – In-Well Air
Stripping/Groundwater Circulating Wells
In-well air stripping involves using air stripping wells to physically remove VOCs from the groundwater. Limited aerobic
biodegradation may also occur within the aquifer due to aeration
of the water around the stripping well. The simplest implementation of in-well air stripping is to inject air under pressure
at the bottom of a well. The well acts as a small stripping column where contaminants in the groundwater partition into the
stripping air. The well is maintained under vacuum to collect the
stripped contaminants.
In-well air stripping is usually combined with groundwater
circulating wells (GCWs) to increase the radius of influence of
the well. Air injected into the well provides stripping action to
volatilize contaminants and air lift pumping to circulate water
around the well. The GCW has two screens, one at the bottom
and the other near the water table, to generate a hydraulically
driven groundwater circulation cell. GCW systems theoretically
create a three-dimensional circulation pattern in the aquifer by
drawing groundwater into the well, pumping it up the well, and
then releasing it into the aquifer without pumping it above
ground. GCW circulation patterns are highly dependent on well
configuration and hydrogeological conditions at a site. A typical
GCW is shown in Figure 1.
Advantages and Limitations
Relative to Air Sparging
FIGURE 1. DIAGRAM OF GCW
In-well air stripping removes VOCs without requiring groundwater extraction and treatment above ground. This eliminates
the need for water discharge permitting. The use of GCWs may
also result in energy cost savings especially at sites with deep
water tables.
The submergence (ratio of the well depth below the water table
to the total depth below the ground surface) of a GCW must be
high enough to ensure a cost-effective groundwater circulation
zone. For generation of an effective circulation zone, GCW
groundwater flowrates must overcome regional groundwater
flows. The effective radius of a well will be severely limited by
a thin heterogeneous aquifer. Seasonal variation of the water
table will greatly influence the recirculating flow and in some
cases stop flow completely. Improperly placed upper and lower
well screens could lead to little or no recirculating flow. Locating upper and lower screens to provide circulation year-round
can be difficult in cases with seasonal variations.
Application of GCW is more sensitive to in situ geology than is
application of air sparging. GCW systems have been tested at
more than 100 locations within the United States and Europe
with documented successes at a few sites; however, the technology is generally not chosen for groundwater cleanup. This is
due to a general lack of knowledge concerning GCWs and also
from mixed results from past applications. It is generally
believed that the technology does not work well at most sites
due to the horizontal (Kh) to vertical (Kv) hydraulic conductivity
ratio (anisotropy) being outside the technology’s applicable
range. The applicable range considered to promote an effective
recirculation zone is 3 to 10 Kh/Kv. Because sites with high
anisotropies (>10 Kh/Kv) are quite common, this technology
appears to have limited application potential. Impermeable soils
will generally result in slow and confining recirculation, where
highly permeable soils may cause short-circuiting. Impermeable
layers between the upper and lower well screens may also prevent the formation of the recirculation zone.
Off-gas collected from the stripping well typically requires
treatment.
Sources for Further Information
Trizinsky, M.A. 1999. “Groundwater Circulating Wells with InWell Air Stripping.” Pollution Engineering. July.
U.S. Environmental Protection Agency. 1998. Field Applications of In Situ Remediation Technologies: Ground-Water
Circulation Wells. EPA/542/R-98/009. Office of Solid
Waste and Emergency Response, Washington, DC.
B-6
SUMMARY SHEET
Air Sparging vs. Monitored Natural Attenuation
Technology Description – Monitored
Natural Attenuation
Monitored natural attenuation (MNA) is an in situ remediation technology that relies on naturally occurring processes to reduce contaminant concentrations in soil and
groundwater. In order to implement MNA, it must be
determined that natural remedial processes will be protective of human health and the environment and achieve
remedial goals within a reasonable time frame.
For MNA, natural subsurface processes such as dilution,
volatilization, biodegradation, adsorption, and chemical
reactions with subsurface materials reduce contaminant
concentrations to acceptable levels. Consideration of this
option often requires modeling and evaluation of contaminant degradation rates and pathways. The primary objective
of site modeling is to demonstrate that natural processes of
contaminant degradation will reduce contaminant concentrations below regulatory standards before potential exposure pathways are completed. In addition, a strict site
monitoring plan must be followed to confirm that contaminant degradation is proceeding at rates and following
pathways that meet cleanup objectives. A typical MNA
scenario is shown in Figure 1.
FIGURE 1. DIAGRAM OF SUBSURFACE NATURAL
ATTENUATION OF A CONTAMINANT PLUME
of contaminants to new media, which can result in new
contaminant exposure pathways.
MNA typically is a lower cost option compared to active
remediation methods such as air sparging. However, MNA
may not be applicable when an expanding plume is
predicted to intercept potential receptors. Remediation
Advantages and Limitations
Relative to Air Sparging
by natural processes can be slow, typically requiring several years to decades, to reach cleanup levels. Land use
controls may be required during implementation of MNA
and data must be collected and analyzed to determine plume
behavior, such as seasonal plume variability, dilution, and
site stratification. It also is possible that intermediate degradation products produced by natural degradation may be
more mobile or more toxic than the original contaminant.
MNA is not the same as “no action,” although it often is
perceived as such. Natural attenuation is considered in the
Superfund program on a case-by-case basis, and guidance
on its use is still evolving. It has been selected at Superfund sites where, for example, polychlorinated biphenyls
(PCBs) are strongly sorbed to deep subsurface soils and
are not migrating; where removal of DNAPLs has been
determined to be technically impracticable (Superfund is
developing technical impracticability [TI] guidance); and
where it has been determined that active remedial measures would be unable to significantly speed remediation
time frames. Where contaminants are expected to remain
in place over long periods of time, TI waivers must be
obtained. In all cases, extensive site characterization is
required.
Sources for Further Information
U.S. Environmental Protection Agency. 1996. A Citizen’s
Guide to Natural Attenuation. EPA/542/F-96/015. Office of
Solid Waste and Emergency Response, Washington, DC.
U.S. Environmental Protection Agency. 1998. Technical Protocol for Evaluating Natural Attenuation of Chlorinated
Solvents in Ground Water. EPA/600/R-98/126. Office of
Research and Development, Washington, DC.
Wiedemeier, T.H., J.T. Wilson, D.H. Kampbell, R.N. Miller,
and J.E. Hansen. 1995. Technical Protocol for Implementing Intrinsic Remediation with Long-Term Monitoring for
Natural Attenuation of Fuel Contamination Dissolved in
Groundwater. U.S. Air Force Center for Environmental
Excellence, San Antonio, TX.
Unlike air sparging, which requires installation of wells
and compressors, MNA allows site remediation with almost
no disturbance of the environment. Short-term risks to
workers and the surrounding population are reduced in
comparison to active remediation. MNA avoids transfer
B-7
SUMMARY SHEET
Air Sparging vs. Phytoremediation
to immobilize or degrade contaminants is not as well tested.
Some volatile organics typically are released with the
transpired water vapor.
Technology Description –
Phytoremediation
Phytoremediation is a soil and groundwater treatment
technology that uses vegetation and its associated microbiota, soil amendments, and agronomic techniques to
remove, contain, or reduce the toxicity of environmental
contaminants. It is generally used as an in situ technology,
but can be used ex situ. Phytoremediation is implemented
by establishing a plant or community of plants that have
been selected to provide the required remediation mechanisms. The technology exploits the natural hydraulic and
metabolic processes of plants, and thus is passive and
solar driven. The technology can be used in combination
with mechanical treatment methods or as a “standalone”
treatment method. Figure 1 shows a conceptual diagram of
a phytoremediation system.
Implementing and maintaining the phytoremediation plantings involves very little disturbance of the site and improves
site aesthetics.
The cleanup time for phytoremediation is longer than that
for air sparging. A growth period of several seasons is
needed for plants to become established and provide full
remedial performance. The rate of remediation is limited
by the plant growth rate. Plantings must be monitored and
managed to ensure that contaminants are not spread off
site by falling leaves or ingested by herbivores.
The depth that can be remediated with phytoremediation is
limited in comparison to the depth that can be treated with
air sparging. Phytoremediation depth is limited to the root
zone (e.g., a few feet for grasses and about 20 ft for trees).
Roots enter the capillary fringe and create a zone of
groundwater depression, but do not extend into the saturated zone, so it can be difficult to treat fast flowing and/or
thick aquifers.
For sites where it is applicable, phytoremediation is
expected to be less costly than air sparging.
Sources for Further Information
Chappell, J. 1997. Phytoremediation of TCE in Groundwater
Using Populus. U.S. Environmental Protection Agency,
Technology Innovation Office, www.clu-in.org/products/
phytotce.htm.
NFESC. 1998. Phytoremediation. TDS-2061-ENV. Naval Facilities Engineering Service Center, Port Hueneme, CA.
FIGURE 1. CONCEPTUAL DIAGRAM OF
PHYTOREMEDIATION SYSTEM
Schnoor, J.L. 1997. Phytoremediation. TE-80-01. Ground-Water
Remediation Technologies Analysis Center, Pittsburgh PA.
Advantages and Limitations
Relative to Air Sparging
U.S. Environmental Protection Agency. 1998. A Citizen’s Guide
to Phytoremediation. EPA/542/F-98/011. Office of Solid
Waste and Emergency Response, Washington, DC.
Phytoremediation is an innovative technology with a
limited history of full-scale application. The ability of
plantings to remove water and provide hydraulic control
has been demonstrated in pilot-scale tests, but the ability
U.S. Environmental Protection Agency. 2000. Introduction to
Phytoremediation. EPA/600/R-99/107. Office of Research
and Development, Washington, DC.
B-8
SUMMARY SHEET
Air Sparging vs. Reactive Barriers
Technology Description – Reactive
Barriers
Reactive barrier technology is an in situ groundwater
treatment method that involves installing a vertical barrier
containing a reactive media to intercept and remediate a
contaminant plume. In its simplest form, a treatment barrier consists of a trench placed in the path of a dissolved
contaminant plume. This trench is filled with a reactive
material, such as granular iron to reduce Cr(VI) or to
dechlorinate halogenated organics, chelators to sequester
selected metals, or other treatment media. As the groundwater passes through the treatment barrier, the contaminants react with the media. For example, chlorinated
organics that come in contact with elemental iron in a
barrier are degraded to potentially nontoxic dehalogenated
organic compounds and inorganic chloride. Although a
variety of reactive media could be used to treat groundwater contaminants, the most commonly used media are
zero-valent metals, particularly granular iron. Figure 1
shows a conceptual diagram of a reactive barrier.
FIGURE 1. CONCEPTUAL DIAGRAM OF A REACTIVE BARRIER
and expensive to contain. Also, costs of barrier construction increases with increasing plume width or depth. The
cost to install a treatment wall increases significantly at
depths greater than 80 ft.
The capital cost to install a reactive barrier typically is
higher than the cost to install an air sparging system. This
higher initial cost may be offset by lower operating costs;
however, site conditions and remedial objectives will determine if reactive barrier treatment is more cost effective than
air sparging. For example, reactive barriers may be selected
instead of air sparging if the concentrations of the contaminant plume are too low for efficient treatment by air sparging.
Advantages and Limitations
Relative to Air Sparging
Reactive barriers are an innovative technology that have
seen extensive application to treatment of chlorinated
hydrocarbon contaminants in groundwater. The main advantage of this system is that no pumping or aboveground
treatment is required. Treatment occurs entirely in situ as
the contaminated groundwater passively moves through the
barrier. Because there are no aboveground installed structures, the affected property can be put to productive use
while subsurface groundwater is being cleaned up.
It can be difficult to install an effective barrier if the
plume is close to site boundaries or receptors.
Sources for Further Information
Unlike air sparging, which allows considerable flexibility
in well placement to accommodate site features, installing
a reactive barrier requires placing a trench that intercepts
the leading edge of the plume. Geotechnical features, such
as underground utility lines, rocks, or consolidated sediments, can increase the difficulty of installing a barrier.
Construction of the barrier requires site disruption
while the trench is being prepared to receive the
reactive media.
Gavaskar, A. 1998. Permeable Barriers for Groundwater Remediation. Battelle Press, Columbus, OH.
U.S. Environmental Protection Agency. 1996. A Citizen’s Guide
to Treatment Walls. EPA/542/F-96/016. Office of Solid
Waste and Emergency Response, Washington, DC.
U.S. Environmental Protection Agency. 1999. Field Applications of In Situ Remediation Technologies: Permeable
Reactive Barriers. EPA/542/R-99/002. Office of Solid
Waste and Emergency Response, Washington, DC.
The cost to implement a reactive barrier depends greatly on
the size of the plume, because large plumes are difficult
B-9
SUMMARY SHEET
Air Sparging vs. Surfactant-Enhanced Aquifer Remediation (SEAR)
Technology Description – SurfactantEnhanced Aquifer Remediation (SEAR)
Advantages and Limitations
Relative to Air Sparging
Surfactant-enhanced recovery is an in situ treatment process used to increase the aqueous solubility of contaminants in an aquifer for greater pump-and-treat recovery.
The surfactant-enhanced recovery process typically is coupled with conventional pump-and-treat systems to expedite
subsurface remediation. Typical examples of contaminants
requiring the addition of surfactants for pump-and-treat
remediation include dense, nonaqueous-phase liquids
(DNAPLs), which have low aqueous solubilities and may
otherwise require hundreds of years to remediate using
conventional pump-and-treat methods. Increasing DNAPL
aqueous solubility by using surfactants potentially can
reduce remediation time. Recovery of light, nonaqueousphase liquid (LNAPL) also can be increased by the
surfactant-enhanced recovery process. Figure 1 shows a
conceptual diagram of a surfactant-enhanced recovery
system.
Surfactant-enhanced recovery is an innovative technology
that does not have a well-established history of full-scale
application. The technology does not provide in situ treatment, but enhances the effectiveness of contaminant
removal to speed remediation. The use of surfactants can
increase the concentration of contaminants in the extracted
fluid by a factor of 10 or more compared to natural
groundwater. The higher concentration reduces the time
needed to clean the site somewhat in comparison to air
sparging. Site cleanup typically is accomplished in 4 to
8 months.
Surfactant-enhanced recovery requires the injection of surfactants into a contaminated aquifer. Typical systems utilize a pump to extract groundwater at some distance away
from the injection point. The extracted groundwater is
treated ex situ to separate the injected surfactants from the
contaminants and groundwater. Once the surfactants have
separated from the groundwater they can be reinjected into
the subsurface. Surfactants are expensive, making recycle
of the flushing solution essential for maximum costeffectiveness. Contaminants must be separated from the
groundwater and treated prior to discharge of the extracted
groundwater.
Application of surfactant flushing requires more sophisticated site data collection and pilot-scale testing than does
application of air sparging. Development of an effective
surfactant solution requires sophisticated bench- and pilotscale testing at each application site. Regulatory limitations on groundwater injection can limit options available
for additives to increase contaminant solubility (i.e., foodgrade surfactants may be required).
Effective application of surfactant-enhanced recovery depends on the ability to control in situ flows. Complex,
heterogeneous geology increases the difficulty of applying
surfactants. Difficulties will also be encountered with lowpermeability soils.
Although data from full-scale surfactant applications is
sparse, initial data suggests that surfactant flushing is
expensive to implement compared to alternative remedial
technologies. It is unlikely that surfactant-enhanced recovery would be competitive with air sparging unless rapid
remediation of the site is required and the contaminants
are too deep or the aquifer too permeable to allow treatment by thermal methods.
Regulatory limitations on groundwater injection can limit
the ability to recycle the flushing solution.
Sources for Further Information
Lowe, D.F., C.L. Oubre, and C.H. Ward. 1998. Surfactants and
Cosolvents for NAPL Remediation – A Technology Practices Manual. Lewis Publishers, Boca Raton, FL.
FIGURE 1. CONCEPTUAL DIAGRAM OF SEAR
IMPLEMENTATION
U.S. Environmental Protection Agency. 1996. A Citizen’s Guide
to In Situ Soil Flushing. EPA/542/F-96/006. Office of Solid
Waste and Emergency Response, Washington, DC.
B-10
SUMMARY SHEET
Air Sparging vs. In Situ Thermal Treatment
Technology Description – In Situ
Thermal Treatment
In situ thermal treatment options include thermal wells,
six-phase soil heating, and in situ steam injection/extraction. These technologies involve using elevated temperature caused by conductive heating to vaporize VOCs and
SVOCs in contaminated groundwater. Vaporized contaminants and groundwater are collected by vacuum extraction
for treatment on site. Figure 1 shows a conceptual diagram
of a typical in situ thermal treatment system.
The steam injection option involves using elevated temperature caused by flow of a heated fluid to vaporize
VOCs in contaminated groundwater and mobilize contaminants and groundwater for extraction. Vaporized contaminants and groundwater are collected by vacuum extraction
and liquid groundwater is collected by pumping for treatment above ground.
Advantages and Limitations
Relative to Air Sparging
In situ thermal treatment is an innovative technology with
a limited history of full-scale application. All of the
approaches to in situ thermal treatment are more intensive
than air sparging, typically resulting in a cleanup duration
in the range of 8 to 12 weeks. The initial cost to mobilize
and set up equipment for in situ thermal treatment typically is greater than that for air sparging and, even with
the shorter operating duration, the overall cost of heating
technologies typically are higher than the cost for air
sparging. In situ thermal treatment typically would be
selected in favor of air sparging only in cases where rapid
remediation is essential or there is significant quantity of
free-phase DNAPL distributed as ganglia throughout the
saturated zone.
Sources for Further Information
General:
Brown, G. 1997. In Situ Thermal Desorption. www.rtenv.com/
insitu.htm.
FIGURE 1. DIAGRAM OF IN SITU THERMAL TREATMENT OF A
CONTAMINANT PLUME
France-Isetts, P. 1998. “In Situ Thermal Blankets and Wells for
PCB Removal in Tight Clay Soils.” Tech Trends. www.cluin.org/products/newsltrs/ttrend/tt0298.htm.
Thermal well treatment involves using heating elements in
blankets and wells operating at temperatures up to 1,000ºC
to input thermal energy into the soil by conduction.
Vaporized contaminants and groundwater migrate to the
surface and are collected by a blower for treatment by
incineration.
The six-phase soil heating option involves using elevated
temperature caused by internal resistive heating to vaporize VOCs in contaminated groundwater. Vaporized contaminants and groundwater are collected by vacuum
extraction for treatment above ground.
Six-Phase Heating:
U.S. Department of Energy. 1995. Innovative Technology Summary Report: Six Phase Soil Heating. Office of Technology
Development, Washington, DC.
Steam Injection:
Balshaw-Biddle, K. 1998. “Heating Technologies and SVE in
Hydraulic Fractures to Remove Hydrocarbon Fuels.” Tech
Trends. www.clu-in.org/products/newsltrs/ttrend/tt0298.htm.
Cook, K. 1996. “In Situ Steam Extraction Treatment.” In J.R.
Boulding (Ed.), EPA Engineering Sourcebook. pp 133-141.
Ann Arbor Press, Inc., Chelsea, MI.
B-11
SUMMARY SHEET
Air Sparging vs. Two-Phase (Dual-Phase) Extraction
Technology Description – Two-Phase
(Dual-Phase) Extraction
Two-Phase Extraction (TPE) (also known as dual-phase
extraction or vacuum-enhanced extraction) is an in situ
technology that applies a high-vacuum system to simultaneously remove liquid and gas from low permeability or
heterogeneous formations.
Two-phase extraction is used primarily to treat halogenated and nonhalogenated VOCs and nonhalogenated semivolatile organic compounds (SVOCs). Two-phase vacuum
extraction enhances airflow to remediate contaminants in
unsaturated soil and, at the same time, collects groundwater for aboveground treatment.
Two-phase extraction provides airflow through the unsaturated zone to remediate volatile organic compounds
(VOCs) and fuel contaminants by vapor extraction and/or
bioventing. The airflow also extracts groundwater for
treatment above ground. The screen in the two-phase extraction well is positioned in both the unsaturated and
saturated zones. A vacuum applied to the well, using a
drop tube near the water table, extracts soil vapor. The
vapor movement entrains groundwater and carries it up
the tube to the surface. Once above grade, the extracted
vapors and groundwater are separated and treated. The
drop tube is located below the static water level, so the
water-table elevation is lowered, exposing more contaminated soil to remediation by the airflow. A conceptual diagram of a typical two-phase system is shown in Figure 1.
Advantages and Limitations
Relative to Air Sparging
TPE is an innovative technology with a well-established
history of full-scale application. Simultaneous extraction
of groundwater and soil gas allows vapor extraction without the disadvantage of the upwelling of the groundwater
level around the extraction well that can occur in conventional soil vapor extraction. LNAPL extraction typically is
inefficient in heterogeneous or low permeability formations and relies on fortuitous well placement under these
conditions. Subsurface heterogeneity can also interfere
with uniform collection of contaminated groundwater and
aeration of contaminated soil. Combination with complementary technologies (e.g., pump-and-treat) may be required to recover groundwater from high-yielding aquifers.
When containment of vapors/liquids is necessary, the
FIGURE 1. CONCEPTUAL EXAMPLE OF TWO-PHASE
RECOVERY SYSTEM
results are better than those obtained through air sparging.
However, two-phase extraction requires both water treatment and vapor treatment that is not necessarily included
with air sparging.
Capital costs and operating duration for TPE are expected
to be similar to those for air sparging. The overall cost for
TPE could be considerably higher than air sparging if it
requires a complex aboveground treatment for the extracted
groundwater or vapor treatment. TPE can reduce the cost
of groundwater treatment compared to conventional pumping and treatment due to the air stripping action that occurs
in the drop tube. In the single-pump configuration, separating the liquid and vapor streams for treatment can be difficult, particularly if LNAPL is present and the groundwater
chemistry promotes formation of stable emulsions.
Source for Further Information
U.S. EPA. 2000. Dual-Phase Extraction. www.epa.gov/OUST/
cat/dualphas.htm.
B-12
APPENDIX C
PROPERTIES OF SELECTED VOCS
q Vapor pressure is the pressure exerted by a vapor
in equilibrium with its pure liquid phase at a given
temperature. It is a measure of the maximum concentration that a given contaminant will volatilize
into air to form a saturated vapor. The vapor pressure, along with the component mole fraction, can
be used to estimate the equilibrium partitioning of
a contaminant from the NAPL phase to soil vapor.
The equation is as follows:
This appendix includes a summary of physicalchemical properties that impact the fate and transport of
volatile organic compounds in the subsurface.
Table C-1 includes physical-chemical properties for
several VOCs. These properties are useful for general
calculations or simple modeling exercises to estimate
equilibrium partitioning of contaminants from soil and/or
groundwater to the soil vapor phase. These parameters
include the molecular weight, organic carbon partition
coefficient, diffusivity terms, water solubility, physical
state at ambient conditions, Henry’s law constants, and
vapor pressure and are defined as follows:
Ci =
q The organic carbon partition coefficient (Koc,
cm3/g) provides a measure of how readily a contaminant will adsorb to organic matter in soil.
(C-2)
where: Ci
= estimate of contaminant vapor
concentration (mg/L)
= mole fraction of contaminant i in
xi
liquid phase (unitless)
Piv = pure component vapor pressure at
a given phase (atm)
MWi = molecular weight of contaminant i
(mg/mol)
R
= universal gas constant =
0.0821 L-atm/mol-K
T
= absolute temperature (K).
q The diffusivity in air (Da, cm2/s) is a mass transfer
parameter related to the rate of contaminant
molecular diffusion in air.
q The diffusivity in water (Dw, cm2/s) is a mass
transfer parameter related to the rate of contaminant molecular diffusion in water.
q The water solubility is the maximum
concentration at which a pure phase contaminant
will dissolve into water at a given temperature to
form a saturated solution.
Figures C-1 and C-2 show vapor pressure versus
water solubility and provide an illustration of how these
physical-chemical properties impact the fate and transport of a given compound. As water solubility increases,
there is an increasing tendency for the compound to dissolve into and move with groundwater. As the vapor
pressure increases, there is an increasing tendency for
volatilization to be the primary means of contaminant
transport.
Figure C-3 is a graph relating a given contaminant’s
vapor pressure to its aerobic half-life. Aerobic half-life
is the time for 50% of the initial compound concentration to biodegrade under aerobic or oxygenated conditions. The general trend shows that as contaminant vapor
pressure increases, the aerobic half-life decreases. A
contaminant with a high vapor pressure is generally
more bioavailable and therefore is degraded more
readily.
q Henry’s law coefficient is a measure of how
readily a contaminant will partition from a dilute
aqueous phase to a vapor phase. It can be used to
estimate equilibrium partitioning of a contaminant
from groundwater to soil vapor or vice versa. The
law states that the partial pressure of the compound in the gas phase (Px) is proportional to the
concentration of a compound in solution (Cx).
Henry’s law coefficient can be approximated as
the ratio of a compound’s vapor pressure to its
aqueous solubility. Henry’s law is as follows:
Px = KH · Cx
x i × Piv × MWi
R ×T
(C-1)
The units for Henry’s constant are KH,
atm-m3/mol-K.
C-1
(a)
TABLE C-1. Physical-Chemical Constants for Selected Volatile Organic Compounds
C-2
Organic
Carbon
Partition
Coefficient,
Koc
(cm3/g)
5.75E-01
6.20E+01
1.00E+02
1.10E+02
9.00E+00
1.50E+02
2.20E+02
1.50E+01
5.30E+01
3.50E+01
4.70E+02
2.80E+01
3.80E+02
3.80E+02
6.20E+02
5.30E+01
3.80E+01
6.50E+01
3.60E+01
3.80E+01
4.70E+01
2.70E+01
2.00E+02
1.00E+01
1.17E+01
1.20E+03
9.10E+02
7.90E+01
Pure
Component
Water
Solubility,
S
(mg/L)
1.00E+06
1.80E+03
6.74E+03
3.20E+03
1.50E+04
7.93E+02
4.72E+02
5.70E+03
7.92E+03
8.20E+03
4.00E+03
3.40E+03
1.56E+02
1.60E+02
7.38E+01
5.06E+03
8.52E+03
2.25E+03
3.50E+03
6.30E+03
2.80E+03
2.80E+03
1.69E+02
1.30E+04
4.80E+04
3.10E+01
3.10E+02
2.97E+03
Pure
Component
Vapor
Pressure
(mm Hg)
Diffusivity Diffusivity
Henry's Law Henry's Law
Molecula
in Air,
Constant
in Water,
Constant
r
Physical
Da
H
Dw
H′
Compound
(cm2/s)
(cm2/s)
(atm-m3/mol)
Weight
State(c)(d)
(unitless)
Acetone
58
1.24E-01
1.14E-05
V
L
3.88E-05
1.59E-03
180
Benzene(b)
78
8.80E-02
9.80E-06
V
L
5.63E-03
2.34E-01
75
Bromodichloromethane
164
2.98E-02
1.06E-05
V
L
1.60E-03
6.56E-02
NA
Bromoform
253
NV
L
5.32E-04
2.18E-02
5
Bromomethane
95
7.30E-02
1.20E-05
V
G
6.20E-03
2.54E-01
1,444
Carbon tetrachloride(b)
154
7.80E-02
8.80E-06
V
L
2.98E-02
1.24E00
91
Chlorobenzene(b)
113
7.30E-02
8.70E-06
V
L
3.88E-03
1.61E-01
9
Chloroethane
65
1.00E-01
1.00E-05
V
L
1.10E-02
4.51E-01
1,000
Chloroform(b)
119
1.04E-01
1.00E-05
V
L
4.24E-03
1.76E-01
160
Chloromethane
51
1.10E-01
6.50E-06
V
G
2.40E-02
9.84E-01
3,800
(b)
Dibromochloromethane
199
9.60E-02
1.00E-05
V
L
1.16E-03
4.83E-02
NA
Dibromoethane, 1,2188
7.30E-02
8.10E-06
V
L
3.20E-04
1.31E-02
12
Dichlorobenzene, 1,2-(b)
147
6.90E-02
7.90E-06
V
L
1.86E-03
7.72E-02
1
(b)
Dichlorobenzene, 1,3147
6.90E-02
7.90E-06
V
L
3.29E-03
1.37E-01
NA
Dichlorobenzene, 1,4-(b)
147
6.90E-02
7.90E-06
V
S
3.18E-03
1.32E-01
1.3
Dichloroethane, 1,1(b)
99
7.42E-02
1.05E-05
V
L
6.49E-03
2.70E-01
182
(b)
Dichloroethane 1,2
99
1.04E-01
9.90E-06
V
L
1.54E-03
6.39E-02
64
Dichloroethylene, 1,1(b)
97
9.00E-02
1.04E-05
V
L
2.66E-02
1.10E00
500
Dichloroethylene, cis 1,2
97
7.36E-02
1.13E-05
V
L
4.07E-03
1.67E-01
180-265
Dichloroethylene, trans 1,297
7.07E-02
1.19E-05
V
L
9.39E-03
3.85E-01
180-265
(b)
Dichloropropane, 1,2113
7.82E-02
8.73E-06
V
L
2.61E-03
1.09E-01
40
Dichloropropene, 1,3
111
6.26E-02
1.00E-05
V
L
1.77E-02
7.26E-01
28
Ethylbenzene(b)
106
7.50E-02
7.80E-06
V
L
8.52E-3
3.54E-01
7
Methylene chloride(b)
85
1.01E-01
1.17E-05
V
L
2.93E-03
1.22E-01
350
Methyl-tert-butyl ether
85
8.10E-02
9.41E-05
V
L
5.87E-04
2.41E-02
NA
Naphthalene (b)
128
5.90E-02
7.50E-06
V
S
7.80E-04
3.24E-02
0.08
Styrene
104
7.10E-02
8.00E-06
V
L
2.80E-03
1.15E-01
5
Tetrachloroethane, 1,1,1,2168
7.10E-02
7.90E-06
V
L
3.50E-04
1.44E-02
14
Tetrachloroethane, 1,1,2,2(b)
168
7.90E+01
7.10E-02
7.90E-06
2.97E+03
V
L
4.53E-04
1.45E-02
5
Tetrachloroethylene(b)
166
2.70E+02
7.20E-02
8.20E-06
2.00E+02
V
L
1.82E-02
7.58E-01
14
Toluene
92
1.40E+02
8.70E-02
8.60E-06
5.26E+02
V
L
6.60E-03
2.71E-01
21
Trichlorobenzene, 1,2,4(b)
180
1.70E+03
3.00E-02
8.23E-06
3.00E+02
V
L
2.14E-03
8.88E-02
1
(b)
Trichloroethane, 1,1,1
133
1.40E+02
7.80E-02
8.80E-06
1.33E+03
V
L
1.74E-02
7.25E-01
100
Trichloroethane, 1,1,2-(b)
133
7.50E+01
7.80E-02
8.80E-06
4.42E+03
V
L
1.16E-03
4.28E-01
19
Trichloroethylene
131
9.40E+01
7.90E-02
9.10E-06
1.10E+03
V
L
1.03E-02
4.22E-01
58
(b)
Vinyl chloride
63
1.90E+01
1.06E-01
1.23E-06
2.76E+03
V
G/L
1.77E-02
7.34E-01
2,508
Xylenes(b)
106
2.00E+02
7.00E-02
7.80E-06
1.61E+02
V
L
7.349E-3
3.05E-01
7-9
(a) Source: The San Francisco Bay Regional Water Quality Control Board (RWQCB) publication "Application of Risk-Based Screening Levels and Decision Making to Sites with
Impacted Soil and Groundwater" (Interim Final, August 2000).
(b) Henry’s law coefficient for these compounds are from the Equilibrium Partitioning in Closed Systems (EPICs) Model.
(c) Vapor pressures at 68°F from NIOSH Handbook.
(d) Physical state of chemical at ambient conditions (V - volatile, NV - nonvolatile, S - solid, L - liquid, G - gas).
NA= Not available.
FIGURE C-1.
Effect of Properties of Fuel Compounds on In Situ Transport
C-3
C-4
FIGURE C-2.
Vapor Pressure vs. Aqueous Solubility for Selected VOCs
C-5
FIGURE C-3.
Relationship Between Contaminant Vapor Pressure and Aerobic Biodegradability
San Francisco Bay Regional Water Quality Control Board
(RWQCB) publication “Application of Risk-Based Screening Levels and Decision Making to Sites with Impacted
Soil and Groundwater” (Interim Final, August 2000).
References
Engineering and Services Center Tyndall Air Force Base,
Equilibrium Partitioning in Closed Systems (EPICs)
Model from Evaluation and Prediction of Henry’s Law
Constants and Aqueous Solubilities for Solvents and
Hydrocarbon Fuel Components, Volume 1: Technical
Discussion, Florida, September 1987.
U.S. Department of Health and Human Services, Public
Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health,
NIOSH Pocket Guide to Chemical Hazards. June 1997.
C-6
APPENDIX D
SOIL PROPERTIES
This appendix includes typical soil properties that
impact the fate and transport of contaminants in the subsurface.
Table D-1 shows typical values for soil characteristics that govern the transport of contaminants in the
vadose or unsaturated zone. These parameters are generally used as input parameters in soil vapor modeling
programs that estimate contaminant mass transfer from
the soil or groundwater to the vapor phase. This table
can also be used to check field measurements to see if
they fall within reasonable expected ranges. The parameters are described as follows:
formation. The higher the soil vapor permeability,
the less resistance there is to airflow.
q The soil organic carbon fraction, foc, is a measure
of the amount of organic matter present in a given
soil for contaminant adsorption.
Table D-2 shows typical contaminant distributions
for a light hydrocarbon in varying soil types. This table
illustrates the fact that a large percentage of contaminant
mass can be found in the smear zone (up to 99.8%). Air
sparging is an effective means of targeting the smear zone
because the injected air moves vertically up through this
region.
Figure D-1 illustrates the U.S. Soil Conservation
Service classification system for several soil types. It
can be used to classify a given soil based on the percentage of sand, silt, or clay present in the material.
Figure D-2 provides typical hydraulic conductivity
and permeability values for a variety of soil types.
q The soil total porosity, n, provides a measure of how
much void space is available between soil particles.
q The soil water-filled porosity, qw, provides a
measure of how much of the void space is filled
by water in the unsaturated zone.
q The soil vapor permeability, kv, is a measure of
the ability of air to flow through a given soil
TABLE D-1. Range of Selected Soil Properties Relevant to Air Sparging Applications
Description
Symbol
Soil total porosity
n
Soil water-filled porosity
qw
Soil vapor permeability
kv
Soil organic carbon fraction
foc
Soil bulk density
rb
(a) Soil property values excerpted from U.S. EPA (2001).
(a)
Practical Range of Values
3
3
0.34 to 0.53 cm /cm
3
3
0.02 to 0.43 cm /cm
2
-6
-12
10 to 10 cm
0.001 to 0.006
3
1.25 to 1.75 g/cm
TABLE D-2. Mass/Volume Distribution of Spilled Hydrocarbon (Gasoline) at
Six Active Service Stations
Phase
Dissolved
Residual
Free Product
Smear Zone
Soil Type
Spill Age
Site 1
0.2%
38%
0%
61%
Sandy
Old
Site 2
0.3%
72%
3%
24%
Clayey
Old
Site 3
0.002%
48%
50%
2%
Sandy
New
D-1
Site 4
0.1%
0.02%
0%
99.8%
Clayey
Old
Site 5
0.02%
36%
0%
64%
Clayey
Old
Site 6
0.1%
11%
51%
38%
Sandy
New
FIGURE D-1. U.S. Soil Conservation Service Classification Chart Showing Centroid Compositions
(solid circles)
D-2
FIGURE D-2.
Range of Values for Hydraulic Conductivity and Permeability
References
Subsurface Vapor Intrusion into Buildings.” Located at
http://www.epa.gov/oerrpage/superfund/programs/risk/air
model/ guide.pdf.
Boelsma, F., E.C.L. Marnette, C.G.J.M. Pijls, C.C.D.F. van
Ree, K. Vreeken. 1999. In Situ Air Sparging, A Technical
Guide. Geodelft Environmental. Stieltjesweg 2, Delft,
The Netherlands.
U.S. EPA, see United States Environmental Protection Agency.
United States Environmental Protection Agency. 2001. “User’s
Guide for the Johnson and Ettinger (1991) Model for
D-3
APPENDIX E
AIR SPARGING ECONOMICS AND COST ESTIMATING WORKSHEET
E.1 Initial Investment
The two main categories of costs for any technology
are initial investment and operation and maintenance
(O&M). Initial investment costs include expenditures
like additional site characterization, pilot-scale testing,
design, and system construction, while O&M costs can
include monitoring, vapor treatment, and site decommissioning costs. These two categories of costs with
respect to air sparging are discussed in detail in this
appendix. Key variables that affect these costs are depth
of groundwater, depth to base of contamination, area of
groundwater contamination, geology, type of contamination, and treatment duration. Additional design information that affects costs include the spacing of the air
injection and soil vapor extraction wells, air injection
flowrate, air extraction flowrate, and regulatory requirements (e.g., monitoring, permitting, etc.).
The cost evaluation described in this section can be
applied to varying degrees of precision at two stages in
the design of an air sparging system. First, a preliminary
cost evaluation may be conducted during preparation of
the corrective action plan or feasibility study to determine the suitability of a site for an air sparging application. This evaluation would compare the cost of an air
sparging application at the site to the cost of using a
competing technology (see Appendix A for the competing technologies matrix). Although a detailed cost evaluation may not be possible at this stage, rough estimates
for initial and O&M costs can be developed. This early
process of cost evaluation also helps to identify the most
cost-effective air sparging construction technique for a
given hydraulic conductivity, contaminant depth, and
other site features involved. NFESC currently is working on an Internet-based program called the Remediation Technology Evaluation Tool (ETET), which will
provide useful features for technology evaluation and
preliminary cost estimating. If the preliminary cost evaluation turns out to be favorable for air sparging, site
managers could proceed to pilot testing, engineering
design, and construction, as described in Section 4.0 of
the main document. Once the draft design is ready, contractors can be contacted to obtain detailed cost estimates,
and a detailed cost analysis then can be conducted.
Initial investment in a technology refers to the funds
required to cover the initial nonrecurring cost involved
in acquiring and installing the technology to the point
where it is ready for its intended use. The initial investment for installing an air sparging system includes the
following major items:
q
q
q
q
Site characterization costs
Pilot-scale testing costs
Design costs
System construction costs.
E.1.1 Site Characterization Costs
Site characterization costs include collecting and
analyzing soil and groundwater samples, as well as evaluating site geology, hydrogeology, and hydrology.
These activities can be a substantial component of remediation costs, whether for air sparging or any other alternative. Given the fact that the effective radius of air
injection wells is strongly influenced by site conditions,
adequate site characterization is all the more important
for understanding the local contaminant and groundwater conditions of the site on the scale of the planned
air sparging system. The degree of site characterization
required at a site may vary depending on the extent of
contamination, complexity of the subsurface environment, and on the amount of existing information available from previous site assessment activities or remedial
investigations/feasibility studies (RI/FS).
E.1.2 Pilot-Scale Testing Costs
Because of the uncertainty inherent with any in situ
treatment technology, a pilot test is needed to evaluate
air sparging feasibility and to collect design basis information prior to detailed design of the full-scale system.
Pilot-scale testing is used to determine site-specific
design parameters such as optimal air injection pressure
and flowrate, air extraction vacuum and flowrate, off-gas
E-1
system. The O&M costs of an air sparging system
include the following major items:
concentrations, the effective sparging radius, the effective vapor extraction radius, and vadose zone biodegradation capacity. The sparging and vapor extraction radii
control the spacing of the air injection and extraction
wells and thus the number of wells needed to effectively
remediate the area. Off-gas concentrations are needed to
determine the most cost-effective vapor treatment approach, and biodegradation capacity is important if the
soil vapor extraction will not be implemented.
Costs for pilot testing include labor, materials and
equipment to install test wells and monitoring points,
conduct testing protocols, and collect/analyze samples.
Pilot testing usually requires 1 to 2 weeks of fieldwork.
q
q
q
q
Contaminant monitoring costs
Performance monitoring costs
Equipment rental and maintenance costs
Site decommissioning costs.
E.2.1 Contaminant Monitoring Costs
These costs may vary from site to site depending on
regulatory requirements, number of monitoring wells, and
frequency of sampling. These costs include sampling,
laboratory analysis, reporting, and labor. Typically, contaminant monitoring is conducted quarterly during air
sparging operation.
E.1.3 System Design Costs
System design and subsequent regulatory review are
important activities that will require some effort and
labor costs. Design generally includes the analyses conducted to interpret site assessment and pilot test data to
determine the location, orientation, configuration, and
dimensions of the air sparging system.
Regulatory requirements can significantly influence
the system design. Meeting stringent treatment criteria
will require closer well spacing or increased operating
time, both of which increase the cost. Also, in jurisdictions with stringent requirements on air releases, it
may be necessary to install a soil vapor extraction system to collect sparged air and an off-gas treatment system
to treat contaminants collected by the SVE system.
E.2.2 Performance Monitoring Costs
If additional monitoring is desired by site managers
to achieve other performance monitoring objectives (see
Section 5.3 of the main document), additional monitoring costs may be incurred. These costs will vary depending on the objectives of site managers at a given site.
For example, if vapor extraction and treatment is
required at the site, periodic off-gas contaminant concentration measurements may be required.
E.2.3 Equipment Rental and Maintenance
Costs
The air sparging system is mechanically simple, consisting of wells, piping, and compressors, so the annual
O&M cost requirements are relatively low. The addition
of a vapor collection and treatment system will significantly increase operating complexity and costs. Rental
costs may be incurred for the vapor treatment system
(e.g., catalytic oxidation, activated carbon, etc.), meters,
compressors, etc. Maintenance costs for an air sparging
system include labor and equipment necessary to service
equipment, such as compressors, blowers, and other
treatment equipment. Also, utility costs for operating the
air sparging system are included in this cost category.
E.1.4 System Construction Costs
System construction costs include labor, materials,
and equipment necessary to install a full-scale air sparging system. Major components of system construction
costs include well installation (i.e., air sparging, soil
vapor extraction, and monitoring wells), sampling and
analysis, compressor(s) to deliver air to the subsurface,
vapor extraction and treatment equipment, support facilities, utility connections, construction materials (e.g.,
piping, fittings, etc.), and labor. Depending on the size
and complexity of the system, construction duration typically ranges from as short as two weeks to as long as
two months.
E.2.4 Site Decommissioning Costs
Upon completion of the air sparging at a site, site
closeout activities will result in identifiable costs. These
activities include system removal and equipment demobilization, well abandonment, labor, and reporting.
E.2 Operating and Maintenance Costs
The O&M costs of a technology are the recurring or
periodic costs incurred during the operating life of the
E-2
required air sparging and SVE well spacing, along with
other site-specific factors. These basic parameters are
then used to estimate the costs for pilot scale testing, construction, operation and maintenance, and site decommissioning. The Air Sparging Cost Estimate Worksheet
is based on the assumptions provided in Table E-1. This
table provides a step-by-step guide to the assumptions for
each cost model item. The assumptions include information about air sparging system design, unit material
and labor costs, labor hours, and other important cost
considerations.
E.3 Air Sparging Cost Estimate
Worksheet
A worksheet for preparing a preliminary cost estimate for an air sparging project is provided in this
appendix. This worksheet does not address site characterization costs because it is assumed that these data will
be required for any remediation technology and are not
specific to air sparging. The air sparging cost model is
based on cost driving parameters such as the depth to
groundwater, the size of the target treatment area, the
TABLE E-1. Assumptions Associated with the Air Sparging Cost Estimate Worksheet
Item
No.
(a)
(b)
(c)
(d)
Parameter
Depth to Groundwater, ft
Area of Groundwater Plume, acres
Air Sparging Well Spacing (Rw), ft
Associated Assumptions
Cost Driving Parameters
Site-Specific Parameter
Site-Specific Parameter
Site-Specific Parameter. Assumptions are provided for
different soil types.
If unknown, assume:
Rw= 15 ft
Number of Air Sparging Wells
2
[Assume 17,900 ´ (b) ¸ (c) ]
Number of wells is a function of area of contamination and the
standard well spacing. The following equation is used:
Number of Sparge Wells =
1.3 A
pR 2w
2
(e)
Installation Depth of Sparge Wells, ft bgs
[Assume (a) + 10 ft]
(f)
SVE Radius of Influence (R), ft
(g)
If unknown, assume based on soil type:
Gravel/Coarse Sand: R = 30 ft
Sand: R = 25 ft
Sandy Silt/Clay: R = 20 ft
Number of SVE Wells
2
[If remediating VOCs, assume 17,900 ´ (b) ¸ (f) .
Otherwise Assume 0]
where A = Area of Contamination (ft )
R = Standard Well Spacing (ft)
17,900 = 1.3 ´ 43,560 ¸ p
Site-Specific Parameter. Wells should be installed below the
lowest depth of contamination. The assumption adds 10 ft to
the depth to groundwater.
Site-Specific Parameter. Assumptions are provided for
different soil types.
Number of wells is a function of area of contamination, SVE
ROI, and whether or not an SVE system is necessary. The
following equation is used:
Number of SVE Wells =
(h)
Installation Depth of SVE Wells, ft bgs
[Assume = (a)]
(i)
Number of Monitoring Wells
[Assume 10 ´ (b)]
(j)
Installation Depth of Monitoring Wells, ft bgs
[Assume (a) + 10]
1.3 A
pR 2
2
where A = Area of Contamination (ft )
R = SVE ROI
17,900 = 1.3 ´ 43,560 ¸ p
Site-Specific Parameter. Wells are typically installed to the top
of the water table. The assumption is the depth to
groundwater.
Site-Specific Parameter. Number of monitoring wells may be
subject to regulatory requirements. The assumption provides
10 wells per acre.
Site-Specific Parameter. The assumption is that monitoring
wells will extend 10 ft below groundwater surface.
E-3
TABLE E-1.
Item
No.
(k)
(l)
(m)
Assumptions Associated with the Air Sparging Cost Estimate Worksheet (continued)
Parameter
Air Injection Flowrate, cfm
[Assume 10 ´ (d)]
SVE Extraction Flowrate [If remediating VOCs,
assume 3 ´ (k). Otherwise Assume 0]
Operation and Maintenance Duration, years
(Assume 1.5 years)
Associated Assumptions
Assumed to be 10 cfm per air sparging well.
If SVE is necessary, the extraction flowrate is assumed to be 3
times the air injection flowrate.
Typical operation and maintenance durations for air sparging
systems range between 1 and 2 years.
Cost Estimating
Pilot-Scale Testing
(n)
Sparging, SVE, and Monitoring Point Installations [$]
= 1,250 + 28 ´ [(e)+(g)] + 60 ´ (a)
(o)
Equipment, Materials, Sampling, and Analytical
Services = $12,000
(p)
Labor = $23,000
·
·
·
·
·
·
·
·
·
·
Construction Costs
(q)
Air Sparging Well Installation [$] = 1,250 + 28 ´ (d) ´
(e)
·
·
·
·
·
·
·
·
·
·
·
·
(r)
SVE Well Installation [$] = 28 ´ (g) ´ (h)
(s)
Monitoring Well Installation [$] = 35 ´ (i) ´ (j)
(t)
(u)
Sampling and Analysis [$] = 400 ´ (d)
Equipment and Materials [$] = 2,000 + 10,000 ´ (b)
(v)
(w)
(x)
Air Compressor(s) [$] = 200 ´ (k)
Off-Gas Treatment System Mobilization and Setup [$]
= 5 ´ (l)
Support Facility(ies) [$] = 5,000 + 40 ´ (k)
(y)
Electrical/Power Connections = $15,000
(z)
Field Labor [$] = 1,800 ´ (d)
·
·
Reporting and Project Management Labor = $10,000
·
(aa)
Operating and Maintenance Cost
(bb)
Off-Gas Treatment [$] = (54 + 10 ´ [(m) ´ 12 - 3]) ´
(l)
·
·
·
·
·
(cc)
Sampling and Analysis [$] = 9,600 ´ (m)
·
E-4
1 Sparge well, 1 SVE Well, if necessary, and 3 monitoring
points
$1,250 mobilization cost
$28 per foot for Sparge and SVE Wells
$20 per foot for monitoring points
Includes disposal of drill cuttings
$8,000 for piping, sampling materials, etc.
$2,000 for air sampling (5 samples at $400 each)
$2,000 for soil sampling (10 samples at $200 each)
Field Labor: 100 hours each for technician and project
engineer/geologist
Reporting/Management: 20 hours for Project
Superintendent, 80 hours for Project Engineer, 40 hours
for Staff Engineer, 20 hours for QA/support
$1,250 mobilization cost
$28 per foot for well installation
Includes disposal of drill cuttings
$28 per foot for well installation
Includes disposal of drill cuttings
$35 per foot for well installation
Includes disposal of drill cuttings
2 soil samples per sparge well at $200 each
$2,000 fixed materials costs
$10,000 per acre of site
$25,000 per 125 cfm of total injection flowrate
If SVE is necessary, $2,500 per 500 cfm extraction
flowrate
$5,000 fixed costs
$5,000 per 125 cfm of total inject flowrate
$15,000 to make electrical/power connections (typically
3-phase 460 volt service)
Labor markup (multiplier) = 2.75
10 hours/Sparge well each for two technicians and one
project engineer/geologist
Reporting/Management: 20 hours for Project
Superintendent, 80 hours for Project Engineer, 40 hours
for Staff Engineer, 20 hours for QA/support
Catalytic Oxidizer for 3 months at $9,000 per month per
500 cfm total extraction flowrate (9,000 ´ 3 ¸ 500 = 54)
Granular Activated Carbon for remainder of project
duration at $5,000 per month per 500 cfm total extraction
flowrate (5,000 ¸ 500 = 10)
2 air samples per month at $400 each
(2 ´ 12 ´ 400 = 9,600)
TABLE E-1.
Item
No.
(dd)
Assumptions Associated with the Air Sparging Cost Estimate Worksheet (continued)
Parameter
Electric [$] = 500 ´ (m) ´ ((k) ¸ 3,125 + (l) ¸ 5,000)
·
·
·
·
(ee)
(ff)
Maintenance [$] = 6,000 ´ (m)
Groundwater Monitoring [$] = 10,000 ´ (i) ´ (m)
·
·
·
(gg)
Field Labor [$] = 22,900 ´ (m)
(hh)
Reporting and Project Management Labor [$] =
27,350 ´ (m)
·
·
·
·
System Closeout Costs
(ii)
System Removal/Demobilization [$] = 5,000 + 5,000
´ (b)
(jj)
Well Abandonment [$] = 1,250 + 20 ´ [(d) ´ (e) + (g)
´ (h) + (i) ´ (j)]
(kk)
Field Labor [$] = 18,000 ´ (b)
(ll)
Reporting and Management Labor = $20,000
·
·
·
·
·
·
·
·
E-5
Associated Assumptions
$0.08/kW-h (0.08 ´ 24 ´ 350 ´ 0.7475 = 500)
System operating 24 hours a day, 350 days per year
25 hp per 125 cfm total air injection flowrate
(25 ´ 125 = 3,125)
10 hp per 500 cfm total air extraction flowrate
(10 ´ 500 = 5,000)
$6,000/year
Quarterly sampling during system operation
$2,500/monitoring well per sampling event
(4 ´ 2,500 = 10,000)
Labor markup (multiplier) = 2.75
8 hours/week for one technician
Labor markup (multiplier) = 2.75
4 hours/month for Project Superintendent, 16 hours/month
for Project Engineer, 8 hours/month for Staff Engineer,
8 hours/month Clerical
$5,000 fixed cost
$5,000 per acre
$1,250 mobilization cost
$20/foot
Labor markup (multiplier) = 2.75
100 hours/acre each for two technicians and one project
engineer/geologist
Labor markup (multiplier) = 2.75
20 hours for Project Superintendent, 80 hours for Project
Engineer, 40 hours for Staff Engineer, 20 hours for
QA/support
Air Sparging Cost Estimate Worksheet
This worksheet provides a method for estimating the capital and O&M costs for a typical air sparging project.
Table E-1 can be consulted for more background information on the assumptions that went into developing the
equations used in this basic cost model.
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(i)
(j)
(k)
(l)
(m)
Cost Driving Parameters
Depth to Groundwater
Area of Groundwater Plume
Air Sparging Well Spacing (Rw)
If unknown, assume based on soil type:
Gravel/Coarse Sand: Rw = 20 feet
Sand: Rw = 15 feet
Sandy Silt/Clay: Rw = 7.5 feet
Number of Sparge Wells [Assume 17,900 ´ (b) ¸ (c)2]
Installation Depth of Sparge Wells [Assume (a) + 10]
SVE Radius of Influence (R)
If unknown, assume based on soil type:
Gravel/Coarse Sand: R = 30 feet
Sand: R = 25 feet
Sandy Silt/Clay: R = 20 feet
Number of SVE Wells [If remediating VOCs, assume 17,900 ´
(b) ¸ (6)2. Otherwise Assume 0]
Installation Depth of SVE Wells [Assume = (a)]
Number of Monitoring Wells [Assume 10 ´ (b)]
Installation Depth of Monitoring Wells [Assume (a) + 10]
Air Injection Flowrate [Assume 10 ´ (d)]
SVE Extraction Flowrate [If remediating VOCs, assume 3 ´ (k).
Otherwise assume 0]
Operation and Maintenance Duration (Assume 1.5 years)
Cost Estimating
Pilot-Scale Testing Costs
(n)
(o)
(p)
Sparge, SVE, and Monitoring Point Installations =
1,250 + 28 ´ [(e)+(g)] + 60 ´ (a)
Equipment, Materials, Sampling, and Analytical Services = $12,000
Labor = $23,000
Installation/Construction Costs
(q)
(r)
(s)
(t)
(u)
(v)
(w)
Air Sparging Well Installation = 1,250 + 28 ´ (d) ´ (e)
SVE Well Installation = 28 ´ (g) ´ (h)
Monitoring Well Installation = 35 ´ (i) ´ (j)
Sampling and Analysis = 370 ´ (d)
Equipment and Materials = 2,000 + 10,000 ´ (b)
Air Compressor(s) = 200 ´ (k)
Off-Gas Treatment System Mobilization and Setup = 5 ´ (l)
E-6
feet bgs
acre(s)
feet
feet bgs
feet
feet bgs
feet bgs
cfm
cfm
years
(x)
(y)
(z)
(aa)
Support Facility(ies) = 5,000 + 40 ´ (k)
Electrical/Power Connections = $15,000
Field Labor = 1,800 ´ (d)
Reporting and Project Management Labor = $10,000
Operation and Maintenance Costs
(bb)
(cc)
(dd)
(ee)
(ff)
(gg)
(hh)
Off-Gas Treatment = (54 + 10 ´ [(m) ´ 12 – 3]) ´ (l)
Sampling and Analysis = 9,600 ´ (13)
Electric = 500 ´ (m) ´ ((k) ¸ 3125 + (l) ¸ 5,000)
Maintenance = 6,000 ´ (m)
Groundwater Monitoring = 10,000 ´ (i) ´ (m)
Field Labor = 22,900 ´ (m)
Reporting and Project Management Labor = 27,350 ´ (m)
System Closeout Costs
(ii)
(jj)
(kk)
(ll)
System Removal/Demobilization = 5,000 + 5,000 ´ (b)
Well Abandonment = 1,250 + 20 ´ [(d) ´ (e) + (g) ´ (h) + (i) ´ (j)]
Field Labor = 18,000 ´ (b)
Reporting and Management Labor = 20,000
Cost Totals
(mm)
(nn)
(oo)
(pp)
(qq)
(rr)
Total – Pilot-Scale Testing = Sum of (n) through (p)
Total – Installation/Construction = Sum of (q) through (aa)
Total – Operation and Maintenance = Sum of (bb) through (hh)
Total – System Closeout = Sum of (ii) through (ll)
System Design = 0.10 ´ [(mm) + (nn)]
Travel = 0.05 ´ [(mm) + (nn) + (oo) + (pp)]
Grand Total = (mm) + (nn) + (oo) + (pp) + (qq) + (rr)
E-7
APPENDIX F
OVERVIEW OF APPLICABLE FEDERAL ENVIRONMENTAL REGULATIONS
F.1 Introduction
(3)
(4)
(5)
(6)
(7)
(8)
The following sections provide brief descriptions of
the federal regulations relevant to the implementation of
air sparging remediation projects as well as a summary
of the potential responsibilities generated by each act. It
should be noted that administration of these federal laws
often has been delegated to the individual states. In some
cases, state laws may exist that are more stringent than
the corresponding federal laws. Please refer to Section
3.0 for a discussion of relevant state/local regulations.
Listing on the NPL
Remedial investigation and feasibility study
Record of decision
Remedial design
Remedial action
Long-term operation and maintenance.
The following is a list of potential responsibilities
generated by CERCLA requirements:
q Conduct remedial investigation and feasibility
study.
F.1.1 Comprehensive Environmental
Response, Compensation,
and Liability Act (CERCLA)
q Propose remedial action and provide opportunities
for public comment.
q Implement remedial action.
CERCLA, also known as the Superfund Act, provides for the identification and remediation of abandoned or uncontrolled hazardous waste sites. CERCLA
regulations apply only to those sites listed on the
National Priorities List (NPL). Remediation of a Superfund site is carried out by the Environmental Protection
Agency in accordance with the procedures and standards outlined in the National Oil and Hazardous Substances Pollution Contingency Plan (NCP). Current or
former owners and operators of the affected sites are liable for the cleanup costs. At federally owned sites, the
federal agency in charge of that facility is responsible
for oversight and implementation of the remediation
project. The requirements of CERCLA are extensive
and a complete discussion of the regulatory implications
is beyond the scope of this manual. The CERCLA regulations covering environmental remediation are included
in 40 CFR Parts 300-311, 355, and 373. CERCLA was
amended in 1986 through the Superfund Amendments
and Reauthorization Act (SARA). SARA streamlined
the Superfund process by simplifying various aspects of
the CERCLA regulation. SARA also contained provisions for community right-to-know laws, which are discussed in Section F.1.2. The following steps generally
are followed during the Superfund process:
q Perform system operation and maintenance.
q Maintain institutional controls, such as zoning
restrictions, water use restrictions, and well
drilling prohibitions.
F.1.2 Emergency Planning and
Community Right-to-Know Act
(EPCRA)
The goal of EPCRA is to promote emergency planning for chemical releases and to provide citizens with
information about chemical hazards in their community.
Under EPCRA rules, the U.S. EPA is required to establish a publicly available toxic chemical release inventory
(TRI) which tracks chemical releases and waste management information from major facilities. The EPCRA
regulations are included in 40 CFR Parts 302, 355, 370,
and 372.
The following is a potential responsibility generated
by EPCRA requirements:
q Track wastes generated during the investigation
and remediation phase and include in facility’s
toxic chemical release inventory (EPCRA
Reporting Form R or Form A).
(1) Preliminary site assessment
(2) Site investigation
F-1
F.1.3 Resource Conservation and
Recovery Act (RCRA)
q Follow all federal, state, and local pretreatment
standards for POTW discharges.
The goal of RCRA is to regulate hazardous waste
management activities. If a remediation project generates hazardous waste, then certain waste management
provisions of RCRA should be followed. Hazardous
waste is defined as materials that contain the constituents listed in RCRA Subtitle C or materials that exhibit
hazardous characteristics, including ignitability, corrosivity, reactivity, and toxicity. At facilities permitted to
manage or dispose of hazardous wastes, certain RCRA
provisions will require corrective action when point-ofcompliance wells at solid waste management units are
above the permitted groundwater protection standards.
The corrective action requirements of RCRA are extensive and a complete discussion of the regulatory implications is beyond the scope of this manual. The RCRA
regulations are included in 40 CFR Parts 240-282.
The following is a list of potential responsibilities
generated by RCRA requirements:
q Apply for 40 CFR Part 404 dredge and fill permits
for construction projects at wetland sites.
F.1.5 Safe Drinking Water Act (SDWA)
The SDWA sets standards for the permissible level
of contaminants in drinking water and establishes treatment standards for drinking water supply systems. If the
affected groundwater at an air sparging site is a current
or potential drinking water source, then the project may
have to meet maximum contaminant levels (MCLs) or
maximum contaminant level goals (MCLGs) for protection of the groundwater source. The SDWA regulations
are included in 40 CFR Parts 141-149.
The following is a potential responsibility generated
by SDWA requirements:
q Meet MCLs or MCLGs to protect groundwater
source and achieve site closure.
q Perform corrective action at out-of-compliance
solid waste management units.
F.1.6 Clean Air Act (CAA)
The CAA regulates point source and mobile source
emissions and sets ambient air quality standards. For air
sparging and soil vapor extraction projects, off-gas treatment is usually required and will involve the control of
volatile organic carbon emissions via thermal oxidation,
catalytic oxidation, carbon adsorption, or other technologies. The CAA requirements will be relevant to the
operation of these air pollution control devices. The permits to operate air pollution control equipment are
issued at the state or local level and the typical components of these permits will be discussed in the section on
state and local regulations. However, the state or local
agencies authorized to issue permits must make sure
that the permits comply with certain CAA provisions.
Only Title I and Title III of CAA are likely to directly
impact air sparging remediation projects. Title I of the
Act requires states to identify areas that have not
achieved National Ambient Air Quality Standards
(NAAQS) for certain critical air pollutants. If the project
is in a nonattainment area, it may be subject to additional emission control standards as outlined in the State
Implementation Plan (SIP). Title III of the Act specifies
point source standards for hazardous air pollutants. For
all sources that emit HAPs, the EPA sets Maximum
Achievable Control Technology (MACT) standards.
q Identify, characterize, and label hazardous waste.
q Manifest hazardous waste for off-site disposal.
q Maintain required records and documentation.
q Ensure that land disposal restrictions are followed.
q Ship wastes within mandated time limits.
F.1.4 Clean Water Act (CWA)
The CWA sets surface water quality standards and
permit requirements for the treatment and discharge of
wastewater and stormwater. The CWA will have limited
applicability to air sparging remediation projects, except
for those projects where liquid wastes are disposed of
via a sewer hookup to a publicly owned treatment works
(POTW). Liquid wastes generated at air sparging sites
can include recovered groundwater, monitoring well
purge water, and knockout tank condensate. The CWA
regulations are included in 40 CFR Parts 100-136, 140,
230-233, 401-471, and 501-503.
The following is a list of potential responsibilities
generated by CWA requirements:
F-2
F.2.1 Endangered Species Act (ESA)
The CAA regulations are included in 40 CFR Parts 5099.
The following is a list of potential responsibilities
generated by CAA requirements:
The ESA includes provisions to conserve endangered or threatened species. Remediation projects must
not destroy or adversely modify critical habitat areas.
The U.S. Fish and Wildlife Service or National Marine
Fisheries Service must be contacted when proposed activities may affect listed species. The ESA regulations are
included in 40 CFR Parts 200 and 402.
q Obtain the necessary permits for air pollution
control equipment.
q Maintain emissions within permitted levels.
q Comply with SIP requirements.
F.2.2 Executive Order Number 11988,
Floodplain Management
q Maintain all required records and documentation.
Federal agencies are required to avoid the adverse
effects associated with construction or development in a
floodplain. An Environmental Impact Statement (EIS)
should be prepared and mitigation may be necessary to
restore and preserve natural resources such as wetlands.
F.1.7 Occupational Safety and Health
Administration Rules (OSHA)
OSHA requires that all work performed on a hazardous waste site be in compliance with a site-specific
health and safety plan (HASP) as described in 29 CFR
1910.120. If a site-specific HASP has not yet been
prepared, it should be and should address all hazards
associated with the site and activities thereon. If a sitespecific HASP has already been developed but does not
address hazards associated with air sparging, an amendment should be made to the HASP (typically regarded
as a “living” document) to include those hazards. One
safety concern particular to air sparging is the migration
of vapors into subsurface structures or occupied surface
structures. If these types of structures are within the
zone of influence of an air sparging system, then an air
extraction or injection system can be used to conduct
vapors away from sensitive areas and prevent the accumulation of explosive or toxic vapors in these structures.
Another safety issue related to air sparging is the possible use of a compressor that stores pressurized air. Catastrophic or unintended sudden release of pressurized air
can result in severe injury and hearing damage or loss.
Adequate safeguards must be taken and protective
devices (hearing protection and hard hat) must be worn
around high-pressure equipment.
F.2.3 Executive Order Number 11990,
Protection of Wetlands
The remediation project must minimize the loss,
destruction, or degradation of wetlands.
F.2.4 Federal Insecticide, Fungicide, and
Rodenticide Act (FIFRA)
The goal of FIFRA is to control the sale and use of
pesticides. The FIFRA regulations are included in
40 CFR Parts 150-189. Air sparging projects at sites
with pesticide contamination must follow certain provisions for the disposal of pesticide-containing wastes. At
sites with pesticide contamination, the remedial project
manager should investigate whether or not the pesticide
residues in the subsurface will have an adverse impact
on biodegradation, especially if biosparging is the chosen application.
F.2.5 National Environmental Policy Act
(NEPA)
The goal of NEPA is to ensure that projects conducted by the federal government involve a review and
analysis of anticipated environmental impacts. NEPA
requires an environmental impact statement (EIS) for all
projects that will significantly affect the environment.
The NEPA regulations are included in 40 CFR Parts
1500-1508.
The following is a list of potential responsibilities
generated by NEPA requirements:
F.2 Other Selected Federal Environmental
Laws and Executive Orders
Several other federal regulations and executive orders
may have an impact on the management of air sparging
remediation projects. The following summarizes some
federal regulations and executive orders that could apply
to air sparging remediation projects under certain limited
conditions.
F-3
q If applicable, perform environmental assessment
and prepare an environmental impact statement.
F.2.7 Toxic Substances Control Act (TSCA)
TSCA sets testing requirements and establishes
restrictions on the use of certain hazardous chemicals,
including polychlorinated biphenyls (PCBs), lead, and
asbestos. TSCA contains four titles: Title I – Control of
Toxic Substances; Title II – Asbestos Hazard Emergency
Response; Title III – Indoor Radon Abatement; and Title
IV – Lead Exposure Reduction. The TSCA regulations
are included in 40 CFR Parts 700-799.
The following is a list of potential responsibilities
generated by TSCA requirements:
q Address the EIS findings and propose project
alternatives and mitigation measures.
q Submit plans to state and/or local agencies and
ensure public participation.
F.2.6 National Historic Preservation Act
(NHPA)
NHPA requires a determination of whether or not the
project would impact any district, site, building, structure,
or object listed or eligible to be listed on the National
Register of Historic Places. The NHPA regulations are
included in 36 CFR Part 800. Other related regulations
include the Archaeological Resources Protection Act
(36 CFR Part 65) and the Native American Graves Protection and Repatriation Act (43 CFR Part 10).
q Proper handling, transport, and disposal of PCBs
and PCB-containing material.
q Use of properly trained and certified contractors
for lead abatement projects.
q Proper handling, transport, and disposal of asbestoscontaining materials.
F-4
APPENDIX G
AIR SPARGING PILOT-SCALE TESTING ACTIVITY MATRIX
This appendix provides a table summarizing key
pilot test activities that should be completed in order to
confirm air sparging feasibility and obtain the information necessary to successfully design a full-scale air
sparging system (Leeson et al., 2001). The table is
organized by activity (i.e., baseline sampling) and
briefly describes the method for data collection and the
objective or questions that will be answered by
interpretation of the data.
G-1
TABLE G-1. Summary of Pilot Test Activities
Activity
Baseline
sampling
G-2
Injection
pressure and
flowrate test
Standard
Pilot Test
Approach
X
SiteSpecific
Pilot Test
Approach
X
Dissolved oxygen
Pressure
transducer data
VOCs, O2, and
CO2 concentrations
X
X
X
X
X
X
Initial SVE off-gas
contaminant
concentrations
X
X
Question(s)
Answered
What are aquifer
conditions prior to
air sparging
startup?
Geophysical
measurements
Is it possible to
achieve desired
flowrate at reasonable pressures?
X
X
X
Comments
· It is important to establish baseline measurements for several key parameters in
order to measure the effectiveness of the air sparging system.
· Methods for collecting dissolved oxygen measurements; pressure transducer
measurements; and VOC, and carbon dioxide measurements are described in
Appendix B of the Design Paradigm (Leeson et al., 2001).
· Conduct baseline dissolved oxygen measurements.
· Pressure data should be collected for a long enough period to assess diurnal
changes in water level (e.g., tidal fluctuations) if they are believed to be significant.
· Soil vapor concentrations (including VOCs, O2, and CO2 concentrations) should be
measured prior to air sparging startup. This provides initial contaminant mass
estimates and a measure of microbial activity in the vadose zone.
· If SVE will be utilized during pilot testing, conduct off-gas sampling and analysis; The
SVE system should be operated prior to air sparging startup. This (1) verifies proper
system operation and (2) establishes VOC volatilization rates from the vadose zone
versus the saturated zone.
· Collect baseline geophysical measurements, if geophysical tools will be utilized
during pilot testing.
· Injection pressures should be recorded at three flowrates: 5, 10, and 20 cfm. The air
injection pressure is recorded at the onset of flow as well as every 5 to 10 minutes
until the pressure and flow stabilize. If a flowrate of at least 5 cfm cannot be
achieved without exceeding a safe pressure, air sparging is not feasible at this site.
· The operating pressure is determined by the depth of the air sparging well below the
water table and the permeability of the aquifer.
· The pressure at which fracturing of the aquifer may occur can be estimated by:
Pfracture [psig] = 0.73 * Dsoil
where: D [ft] = depth below ground surface to the top of the air injection well
screened interval.
· Pressures in excess of Pfracture can cause fracturing of the formation; however, as the
pressure drops off rapidly away from an injection point, the extent of fracturing in
most cases is expected to be limited to the area immediately surrounding the well.
TABLE G-1. Summary of Pilot Test Activities (page 2 of 4)
Activity
Groundwater
pressureresponse test
G-3
Helium tracer
test
Question(s)
Answered
What are the
general characteristics of the air
distribution?
a) Semiconical air
distribution in a
homogenous
setting OR
b) Irregular shape
due to significant
stratification.
What is the lateral
extent of the air
distribution? Are
there indications of
preferential
flowpaths?
Standard
Pilot Test
Approach
X
SiteSpecific
Pilot Test
Approach
X
X
X
Comments
· The primary objective of this test is to assess the time required for airflow distribution
to come to steady state.
· Typically, as long as the volume of air below the water table is increasing, the
groundwater pressure will remain above pre-air sparging levels. As a result, the time
required for groundwater pressure to return to pre-air sparging values is a good
measure of the time required for the macro-scale air distribution to come to steady
state.
· For homogeneous media (e.g., uniform sands), the time required for air sparging
pressures to return to pre-air sparging values will generally be measured in tens of
minutes to a few hours. If the site is stratified with lower-permeability layers, then the
groundwater pressure may remain elevated for tens of hours to days.
· Generally, at sites where groundwater pressures remain elevated by more than a few
tens of centimeters for more than 8 hours, it can be assumed that the air distribution
is controlled to a high degree by the structure of the aquifer. It will be important to
determine if the air is being delivered to the treatment area in an effective manner.
· Helium can be used in two primary ways as a tracer for air sparging systems (Leeson
et al., 2001). In both tests, a rechargeable helium leak detector is used to detect
helium at concentrations from 0.01 to 100 percent.
· To characterize the injected air distribution pattern in the subsurface, helium is added
to the sparge air at a known rate to achieve a steady helium concentration of about 2
to 10% by volume. Immediately after helium injection, until 20 minutes have lapsed,
all of the vadose zone monitoring points and groundwater monitoring wells are
monitored for helium. The helium measurements show which portion of the
saturated zone is coming into contact with the injected air.
· To assess the effectiveness of the SVE system in capturing the injected air, helium is
added into the sparge air at a known rate and the SVE off-gas is monitored for the
appearance of helium. Injection should continue until a stable helium concentration
is achieved. The fraction of helium recovered by the SVE system is calculated.
· Helium recovery data tends to fall into two ranges. The sparge air either makes it to
the vadose zone and is collected by the SVE system with a high (e.g., >70%)
recovery, or the air is stratigraphically trapped, pushing it beyond the SVE system or
out monitoring wells, in which case recovery is low (e.g., <20%).
TABLE G-1. Summary of Pilot Test Activities (page 3 of 4)
Activity
Soil-gas
sampling/offgas sampling
Question(s)
Answered
What is the
volatilization rate?
Are there any
obvious safety
hazards?
Standard
Pilot Test
Approach
X
SiteSpecific
Pilot Test
Approach
X
G-4
Dissolved
oxygen (DO)
measurements
What is the
approximate lateral
extent of the air
distribution? Are
there indications of
preferred
directions?
X
X
Other
observations
Are there any
odors, noise, or
other factors
present that make
system operation
less acceptable?
X
X
Comments
· For systems without an SVE system, over the period of the pilot test, soil-gas
samples should be collected with a field handheld instrument appropriate for the
contaminants of concern. The observed values should be compared to the pre-air
sparging concentrations to determine if a significant mass of contaminant is being
stripped out of the groundwater.
· With an SVE system, increases in contaminant concentrations in the SVE off-gas,
and the SVE extraction flowrate can be used to estimate the mass removal rate.
· Measurements made during the short duration of a pilot test are not indicative of
long-term performance. However, it can generally be assumed that the pilot test
data represent the maximum removal rate from the system (pre-optimization). In that
context, if mass removal rates during the pilot test are very low, then there should be
significant concern about the viability of air sparging at the site.
· If the preliminary measurements show low DO concentrations (e.g., less than
2 mg/L), it may be possible to identify areas where air sparging has resulted in
increases in DO. To determine this, dissolved oxygen should be measured in all
groundwater monitoring points immediately following the pilot test.
· At many sites where active biodegradation is ongoing, there may be significant
quantities of reduced species (e.g., Fe(2+)) which act as rapid sinks for oxygen and
masks the delivery of oxygen to that region.
· Microbial consumption of oxygen can be very high, resulting in oxygen being
consumed as rapidly as it reaches an area, and therefore cannot be detected with
instrumentation.
· Care must be taken to avoid artifacts caused by air entry into monitoring wells and
preferential aeration within the well (Johnson et al., 1997).
· It is important to note any qualitative indicators of air distribution, such as bubbling or
gurgling noises in wells, water “fountaining” out of monitoring points, etc.
· It is also important to be aware of odors due to the contaminants, noise due to the
equipment, or other environmental factors.
· These factors may not make air sparging infeasible from a technical standpoint, but
may make the system less acceptable for the community.
TABLE G-1. Summary of Pilot Test Activities (page 4 of 4)
Activity
Question(s)
Answered
What is the vertical
and lateral extent
of the air distribution in the target
treatment zone?
What are the oxygen transfer rates
to groundwater?
Standard
Pilot Test
Approach
SiteSpecific
Pilot Test
Approach
X
Comments
· SF6 is used as a tracer that mimics oxygen to determine the distribution of air in the
groundwater (Johnson et al., 1996).
· SF6 has a water solubility that is similar to oxygen; however, SF6 has several
advantages over oxygen and as a result the test can be both more sensitive and
more quantitative.
· SF6 is blended with the injection air stream at a known concentration for a period of
12 to 24 hours. At the end of the SF6 injection period, groundwater samples are
collected and analyzed for SF6. The duration of SF6 injection and the cumulative
volume of groundwater sample are recorded. Based on the concentration of SF6 in
the injected air, and the Henry’s law constant for SF6, the percent saturation of SF6 in
the groundwater sample can be determined.
· In general, the results can be divided into three groups: (a) values approaching
saturation (e.g., >40% of theoretical solubility) indicate that the sample location lies
within the “zone of aeration” of the air sparging system; (b) samples with low concentrations of SF6 (e.g., <10%) indicate that an air channel may be in the vicinity of the
sampling location (e.g., it may be within the “zone of treatment”) but the air saturation
in the aquifer at that point is probably low; and (c) samples that have no SF6 present
are presumed to lie outside both the aeration and treatment zones.
Other
What is the vertical
Optional
· Air distribution patterns can be measured by the use of neutron probes, capacitance
geophysical
and lateral extent
probes, and electrical resistance tomography as reported in the literature (e.g.,
tools
of the air distribuAcomb et al., 1995; Lundegard and LaBreque 1998). These techniques generally
tion in the target
have the ability to detect the presence of air in the subsurface at the 10% by volume
treatment zone?
level.
· Once again, it is important to remember that all of these techniques require
background (i.e., pre-air sparging) measurements.
Acomb, L.J., D. McKay, P. Currier, S.T. Berglund, T.V. Sherhart, and C.V. Benedicktsson. 1995. Neutron Probe Measurements of Air Saturation Near an
Air Sparging Well. In In Situ Aeration: Air Sparging, Bioventing, and Related Remediation Processes, pp. 47-61. (Hinchee, R.E., R.N. Miller, and P.C.
Johnson, Eds.). Battelle Press: Columbus, Ohio.
Johnson, R.L., R.R. Dupont, and D.A. Graves. 1996. Assessing UST Corrective Action Technologies: Diagnostic Evaluation of In Situ SVE-Based System
Performance. EPA/600/R-96/041.
Johnson, P.C., R.L. Johnson, C. Neaville, E.E. Hansen, S.M. Stearns, and I.J. Dortch. 1997. “An Assessment of Conventional In Situ Air Sparging Pilot
Tests.” Ground Water, 35(5): 765-774.
Lundegard, P.D., and D.J. LaBreque. 1998. “Geophysical and Hydrologic Monitoring of Air Sparging Flow Behavior: Comparison of Two Extreme Sites.”
Remediation (Summer): 59-71.
SF6
distribution
test
G-5
APPENDIX H
TROUBLESHOOTING OPERATIONAL MATRIX
This appendix provides a troubleshooting guide for
common air sparging performance problems. This guide
will help RPMs anticipate common problems, isolate
their cause, and develop potential solutions to improve
air sparging implementation.
TABLE H-1. Air Sparging Troubleshooting and Performance Optimization Guide
Performance Issue
Extent of contamination is greater than
initially expected.
Potential Cause
• Limited initial site investigation.
• Free product is identified.
Groundwater monitoring shows an
increase in VOC
concentrations.
• Sorbed or residual free product
has been liberated for dissolution
into the groundwater.
• Hydraulic mounding may be a
problem at this site causing a
spreading of the contaminant.
Increasing injection
pressure needed to
maintain target
flowrate.
Off-gas treatment
costs increase.
• Injection well biofouling or
plugging.
Air distribution is
limited.
Remediation system
cannot be installed
as planned.
VOC concentrations
reduced in only a
few wells.
VOC recovery by
the SVE system
gradually
decreases.
VOC recovery by
the SVE system
rapidly decreases.
• VOC recovery is declining as
cleanup continues. There is not
enough heat value in the process
gas to maintain autothermic combustion in the thermal/catalytic
oxidizer.
• Poor well construction.
• Soil permeability or preferential
channeling may be a problem.
• Subsurface structures (gas lines,
utility lines, etc.).
• Surface structures (buildings).
• The air sparging may not be
evenly distributed on the site.
• A gradual decrease in VOC concentrations from initial levels is to
be expected. It is due to diffusion
limitations that occur as the
product is cleaned up.
• Flooding of SVE system.
• Check and empty knockout tank(s)
Potential Solution
• Define extent of contamination
• Use free-product recovery methods as necessary (Hoeppel
and Place, 1998).
• Extend the air sparging system by installing new injection/extraction wells focused on source zones.
• The concentrations should decline once the residual or sorbed
contaminants have been sparged.
• Hydraulic mounding can be mitigated by pulsed operation,
which allows the water table levels to return to normal. Pulsed
operation involves cycling the sparge system on and off over
periods of hours to weeks.
• If trend continues over several quarters, modify downgradient
control either via more sparge "barrier" wells or use of groundwater recovery wells.
• Clean well and associated piping.
• Evaluate other air pollution control options including activated
carbon.
• Operate the system in pulsed mode.
• Use other technologies to speed up vapor removal such as
thermal enhancements.
• Check wells for clogging or short-circuiting.
• Another site investigation (helium or other tracer tests) might
be necessary to further assess the location of impermeable
zones or lenses. Adjust well depth or location as appropriate.
• Adjust design to change the number of wells or well density.
• Reevaluate injection/extraction well placement.
• Consider drilling at an angle or installation of horizontal wells
(rare).
• Reduce flow to some wells.
• Check for unidentified source zone.
• Add additional wells.
• Using a pulse operation can improve system performance.
The system can be cycled on and off for periods of hours to
weeks which allows the VOC concentrations to rebound.
• If appropriate, propose shutting down of air sparging/SVE system in favor of monitored natural attenuation.
• Use water level measurements to check water table elevation
with respect to the SVE well screen depth. Temporarily shut
down system until water table drops. If the problem persists,
consider design changes including reinstallation of SVE wells
at a lesser depth or multiphase extraction with liquid/vapor
pumps.
H-1
VOC recovery is at
or near lower
explosive limits.
• Presence of free product.
• Dilute SVE airstream at extraction wellheads.
• Check for free product and use recovery methods as
necessary (Hoeppel and Place, 1998).
Reference
Hoeppel, R., and M. Place. 1998. Application Guide for Bioslurping. NFESC Technical Memorandum No. TM-2300ENV. Prepared for NFESC by Battelle. October.
H-2
APPENDIX I
AIR SPARGING PROJECT STATEMENT OF WORK GUIDANCE
This Statement of Work (SOW) Guide outlines, in
tabular form, the technical information required to define
tasks and performance standards. All of the work elements that might be required to assess and implement an
air sparging treatment system under any one of a wide
range of regulatory frameworks are listed in the tables.
Potentially applicable regulatory frameworks include the
following:
result can be determined. They must be sufficiently
demanding to provide an acceptable result, but not so
demanding as to be uneconomical or impractical. More
detailed information on preparing a performance-based
SOW is available in U.S. Environmental Protection
Agency guidance (U.S. EPA, 1995).
A typical air sparging project starts with a review of
existing data followed by data collection and feasibility
analysis to determine if air sparging is indeed applicable
to a specific site. If it is determined that the technology
is applicable to the site in question, the next step is to
design the system. Following system design and installation is system operation. In addition to running the
system, the operation period also includes system optimization tasks and site monitoring. The final step in the
remedial process is site closure and project closeout.
Tasks in the SOW must be defined to allow input from
regulators and, where necessary, the public through
formal and informal forums frequently throughout the
evaluation and implementation process. The SOW should
require a staged approach to the evaluation and implementation of the remedial action to determine that air
sparging is applicable and will be effective at a site
before making a significant commitment of resources to
this alternative. Once these decisions have been made,
the complexity of the site, contaminant conditions, and
remedial objectives determine the design of the system,
length of system operation, monitoring requirements
and details regarding site closure.
The SOW clearly defines the roles and responsibilities of the participants in the work. Related work that has
been completed as part of a prior project or is to be
performed in parallel under a separate SOW must be
described, and the relation to the planned work explained.
Key decision points and interfaces must be clearly
described so that all participants understand who is to
perform each work element, what is to be done, and
where the authority lies for accepting the results.
The SOW requires the contractor to provide separate costs for each task specified using the Work Breakdown Structure (WBS) specified by the Navy. Having
detailed cost information for each task allows more
effective comparison of the bids. Appendix D of this
guidance document presents a discussion of air sparging
q CERCLA
q Corrective action (CA) provisions of RCRA
q Underground storage tank (UST) provisions of the
RCRA (federally regulated)
q State-regulated or administered UST cleanup
programs.
This document will assist in preparing an SOW that
fosters timely, concise, cost-effective submissions from
potential contractors. Project tasks are grouped into the
following six phases:
q
q
q
q
q
q
Project planning and management
Preliminary assessment of air sparging
Detailed site evaluation and feasibility analysis
System design and installation
System operation and optimization
Long-term monitoring and site closure.
Some of the tasks described may not be required for a
particular site because of site conditions or the regulatory
framework. The personnel preparing the SOW must
select applicable tasks in the tables in Section I.3, and use
the tabulated information to assist in preparing a SOW.
This SOW Guide can be used to develop an SOW
that describes the technical requirements for the project
and to define the basis for evaluating the technical quality and value of a contractor’s proposal. Preparing an
effective SOW requires careful thought and planning to
identify the key tasks that must be performed and the
criteria that must be met without limiting the contractors’ flexibility to provide their best value option. The
criteria must be clearly stated so that the quality of the
I-1
economics and will assist Naval personnel in estimating
costs so they can evaluate the value offered by each
proposal.
This SOW Guide is organized to cover the sections
that appear in a typical SOW, as shown in Figure I-1.
I.1
I.1.1
The SOW must define the regulatory constraints
applicable to the site. In particular, the lead regulatory
agency must be identified. Other interested regulatory
and public interest groups and their relationships to the
project must also be summarized in the SOW.
Scope
I.2 Reference Documents
General
The SOW provides a listing of documents that
describe the data, methods, or requirements applicable
to the work necessary for evaluating and/or implementing air sparging at petroleum hydrocarbon-contaminated
sites. Examples of documents that may be applicable for
sites planning to implement air sparging for petroleum
contamination include the following:
Figure I-2 shows an example of a typical scope
statement for a project to implement air sparging.
I.1.2
Background
An SOW is required when the facility has identified
the need to remediate a site that has groundwater contaminated with strippable or aerobically biodegradable
compounds and is interested in using air sparging. The
SOW must clearly summarize any completed site characterization, review of regulatory constraints, and technical analyses to establish site-specific remediation goals.
Figure I-3 lists the typical background information
summarized in the SOW. This SOW Guide assumes that
efforts under the contract make maximum use of the
existing data and monitoring points installed at the site.
Necessary background information often is contained in
project reports, manuals, and photographs summarizing
the current state of knowledge. These reports can be
attached to the SOW or otherwise made available to the
contractor. If possible, the SOW should allow time for a
site visit by contractors during proposal preparation.
I.2.1
Air Sparging Site Assessment
a. American Society for Testing and Materials. 1997.
“Standard Guide for Corrective Action for
Petroleum Releases.” D 1599. Annual Book of
ASTM Standards, Volume 11.04, ASTM, West
Conshohocken, PA.
b. American Society for Testing and Materials. 1995.
Standard Guide for Risk-Based Corrective Action
Applied at Petroleum Release Sites. ASTM-E 173995. ASTM, West Conshohocken, PA.
c. American Society for Testing and Materials. 1995.
Standard Guide for Developing Conceptual Site
Models for Contaminated Sites. ASTM-E 1689-95,
ASTM, West Conshohocken, PA.
1.0 Scope
1.1 General
1.2 Background
2.0 Reference Documents
3.0 Requirements of the RNA Project
3.1 Project Planning and Management
3.2 Preliminary Assessment of Air Sparging
3.3 Detailed Site Evaluation and Feasibility Analysis
3.4 System Design
3.5 System Operation and Optimization
3.6 Long-Term Monitoring and Site Closure
4.0 Government-Furnished Property
5.0 Government-Furnished Facilities
6.0 Deliverables
FIGURE I-1.
Organization of a Typical Statement of Work
I-2
The purpose of this Statement of Work is to set forth the requirements for implementing remediation by air
sparging in accordance with the provision of
(decision document, e.g., permit issued by the state or
regional water control board, Record of Decision [ROD], or permit modification or order) issued on
(date). The required efforts will include the following:
·
·
·
·
·
·
Project management and planning
Preliminary assessment of air sparging
Detailed site evaluation and feasibility analysis
System design and installation
System operation and optimization
Long-term monitoring and site closure
Air sparging and the related technology of biosparging are defined as follows:
Air sparging is an innovative treatment technology that uses injected air to remove volatile or biodegradable
contaminants from groundwater. Air sparging can remove contaminants such as gasoline, solvents, and
selected jet fuels. The basic process involves the injection of air directly into the saturated subsurface to
(1) volatilize contaminants from the liquid phase to the vapor phase for biodegradation and/or removal via soil
vapor extraction (SVE) in the vadose zone, and (2) degrade contaminants in the saturated zone via microbial
metabolism stimulated by the introduction of oxygen.
This SOW provides the framework for conducting remediation of contaminated groundwater at
(site). The goal is to complete remedial design by
(date) and site closure by
(date).
FIGURE I-2.
Example SOW Scope Statement
§
§
§
§
§
§
§
§
§
§
FIGURE I-3.
Initial site conditions
— Location and physical layout
— Availability of utilities
— Restrictions on access or road use
Documentation of state concurrence with air sparging application to
site
Relevant documents prepared by the local water control board (or
equivalent)
Existing permits
Cleanup standards and regulatory requirements
Nature and extent of contamination
Approximate volume to be remediated
Geomorphology and surface water hydrology
Geology and geohydrology
— Location and types of strata
— Depth to groundwater
— Direction of groundwater flow
Unresolved issues
Example of Site Information Typically Summarized in the SOW
I-3
d. American Society for Testing and Materials. 1997.
“Conceptualization and Characterization of GroundWater Systems.” D 5979. Annual Book of ASTM
Standards, Volume 4.09. ASTM, West
Conshohocken, PA.
e. American Society for Testing and Materials. 1997.
“Standard Guide for Application of a Ground-Water
Flow Model to a Site-Specific Problem.” D 5447.
Annual Book of ASTM Standards, Volume 11.05.
ASTM, West Conshohocken, PA.
f. American Society for Testing and Materials. 1997.
“Standard Guide for Comparing Ground-Water
Flow Model Simulations to Site-Specific Information.” D 5490. Annual Book of ASTM Standards,
Volume 11.05. ASTM, West Conshohocken, PA.
g. American Society for Testing and Materials. 1997.
“Standard Guide for Defining Boundary Conditions
in Ground-Water Flow Modeling.” D 5609. Annual
Book of ASTM Standards, Volume 11.05. ASTM,
West Conshohocken, PA.
h. American Society for Testing and Materials. 1997.
“Standard Guide for Defining Initial Conditions in
Ground-Water Flow Modeling.” D 5610. Annual
Book of ASTM Standards, Volume 11.05. ASTM,
West Conshohocken, PA.
i. American Society for Testing and Materials. 1997.
“Standard Guide for Conducting a Sensitivity
Analysis for a Ground-Water Flow Model Application.” D 5611. Annual Book of ASTM Standards,
Volume 11.05. ASTM, West Conshohocken, PA.
j. U.S. Navy. 1998. “Performance-Based Statement of
Work.” Available from http://www.acqref.navy.mil/turbo/arp34.htm.
I.2.2
d. U.S. Environmental Protection Agency. 1989.
CERCLA Compliance with Other Laws, Part 2.
EPA/540/G-89/009. Office of Solid Waste and
Emergency Response, Washington, DC.
e. U.S. Environmental Protection Agency. 1996.
A Citizen’s Guide to In Situ Soil Flushing. EPA/
542/F-96/006. Office of Solid Waste and Emergency Response, Washington, DC.
f. U.S. Environmental Protection Agency. 1996.
A Citizen’s Guide to Bioremediation. EPA/542/
F-96/007. Office of Solid Waste and Emergency
Response, Washington, DC.
g. U.S. Environmental Protection Agency. 1996.
A Citizen’s Guide to Natural Attenuation. EPA/542/
F-96/015. Office of Solid Waste and Emergency
Response, Washington, DC.
h. U.S. Environmental Protection Agency. 1998. Field
Applications of In Situ Remediation Technologies:
Ground-Water Circulation Wells. EPA/542/R98/009. Office of Solid Waste and Emergency
Response, Washington, DC.
i. U.S. Environmental Protection Agency. 1998. Technical Protocol for Evaluating Natural Attenuation
of Chlorinated Solvents in Ground Water. EPA/600/
R-98/126. Office of Research and Development,
Washington, DC.
I.2.3
System Design and Installation
a. American Society for Testing and Materials. 1997.
“Standard Practice for Design and Installation of
Ground Water Monitoring Wells in Aquifers.”
D 5092. Annual Book of ASTM Standards,
Volume 4.09. ASTM, West Conshohocken, PA.
b. Aelion, C.M., and B.C. Kirtland. (2000). Physical
versus Biological Hydrocarbon Removal during Air
Sparging and Soil Vapor Extraction. Environ. Sci
Technol. v34, no. 15, 3167-3173.
c. Herrling, B. J. Stamm, E.J. Alesi, G. Bott-Breuning,
and S. Diekmann. 1994. “In Situ Bioremediation of
Groundwater Containing Hydrocarbons, Pesticides,
or Nitrate Using Vertical Circulation Flows.” In: Air
Sparging for Site Remediation. R.E. Hinchee (Ed.).
CRC Press, Inc. Boca Raton, FL.
d. Leeson, A., P.C. Johnson, R.L. Johnson, R.E.
Hinchee, and D.B. McWhorter. 2001. Air Sparging
Design Paradigm. In Press. December 31.
e. Marley, M.C., and C.J. Bruell. 1995. In Situ Air
Sparging: Evaluation of Petroleum Industry Sites
and Considerations for Applicability, Design and
Technology Review and Selection
a. U.S. Environmental Protection Agency. 1988.
Guidance for Conducting Remedial Investigations
and Feasibility Studies under CERCLA.
EPA/540/G-89/004. OSWER Directive 9355.3-01.
Office of Solid Waste and Emergency Response,
Washington, DC.
b. U.S. Environmental Protection Agency. 1989.
Guidance for Preparing Superfund Decision
Documents. EPA/540/G-89/007. Office of Solid
Waste and Emergency Response, Washington, DC.
c. U.S. Environmental Protection Agency. 1989.
CERCLA Compliance with Other Laws, Part 1.
EPA/540/G-89/006. Office of Solid Waste and
Emergency Response, Washington, DC.
I-4
q
q
q
q
q
q
Operation, American Petroleum Institute,
Washington, DC, Publication Number 4609.
I.2.4
Performance Monitoring/Site Closeout
a. Tri-Service/U.S. Environmental Protection Agency
Working Group. 1998. Environmental Site Closeout
Process. Working draft.
b. U.S. Environmental Protection Agency. 1992.
Methods for Evaluating the Attainment of Cleanup
Standards, Volume 2: Groundwater. EPA/230/R92/014. Office of Solid Waste and Emergency
Response, Washington, DC.
c. U.S. Environmental Protection Agency. 1989.
Statistical Analysis of Ground-Water Monitoring
Data at RCRA Facilities. EPA/530/SW-89/026.
Office of Solid Waste and Emergency Response,
Washington, DC.
d. American Society for Testing and Materials. 1997.
“Standard Guide for Site Characterization for
Environmental Purposes with Emphasis on Soil,
Rock, the Vadose Zone, and Ground Water.”
D 5730. Annual Book of ASTM Standards, Volume
4.09. ASTM, West Conshohocken, PA.
e. American Society for Testing and Materials. 1997.
“Provisional Standard Guide for Developing
Appropriate Statistical Approaches for GroundWater Detection Monitoring Programs.” PS 64.
Annual Book of ASTM Standards, Volume 4.09.
ASTM, West Conshohocken, PA.
f. American Society for Testing and Materials. 1993.
Standard Guide for Decommissioning of Ground
Water Wells, Vadose Zone Monitoring Devices,
Boreholes, and Other Devices for Environmental
Activities. D 5299-92. ASTM, West Conshohocken,
PA.
g. Naval Facilities Engineering Service Center. 2000a.
Interim Final Guide to Optimal Groundwater
Monitoring. Prepared by Radian International,
White Rock, NM. January. Available at:
http://erb.nfesc.navy.mil/erb_a/support/
wrk_grp/raoltm/case_studies/Int_Final_Guide.pdf.
Project planning and management
Preliminary assessment of air sparging
Detailed site evaluation and feasibility analysis
System design and installation
System operation and optimization
Long-term monitoring and site closure.
The tasks specifically related to implementing air
sparging are tabulated for each phase. Tasks that are
appropriate for a particular site should be selected and
the SOW should then be prepared based on the scope
and typical preparation time, as stated in the tables. The
information provided under the heading “Task Guidance
and Information” in each table can be used to assist in
preparing the SOW and evaluating responses from the
bidders.
I.3.1
Project Planning and Management
The purpose of this project phase is to provide overall management to maximize the effectiveness of expenditures throughout the project. The SOW requires the
contractor to provide the labor, equipment, materials,
and facilities to prepare the required plans and effectively manage the air sparging project. The major tasks
included in this phase are summarized in Table I-1.
Contractors are required to furnish a description of
each of the following project management components
as part of their proposal:
q Overall organizational structure proposed for the
project
q Qualifications of the project management team
q Project management system to be used
q Subcontracting systems to be used
q Relevant corporate experience.
Contractors are required to furnish, as a part of their
proposal, a current corporate Quality Assurance/Quality
Control (QA/QC) Program Plan setting forth their QA/
QC capabilities. The QA/QC Program Plan must address,
at a minimum, the following topics:
I.3 Requirements
The following subsections provide the technical
background about the tasks that are specified in an SOW
to obtain a proposal for implementing air sparging. The
project is divided into the following six phases:
q A statement of the corporate QA/QC policy
q An organization chart showing the position of the
QA/QC function in the organization
I-5
TABLE I-1. Statement of Work Requirements for Air Sparging: Project Planning and
Management
Task Name
Project
management
plan(a)
Community
relations plan(a)
Task Scope
Document overall strategy,
budget, and schedule for
performing the design,
installation, performance
monitoring, and close out of
air sparging project
Plan for information transfer
and consensus building with
local representatives, as
necessary
Task Guidance and Information
· Document responsibility and authorities of all
organizations
· Identify key personnel
· Document qualifications of key personnel
· Reflect knowledge of citizen concerns
· Provide for citizen involvement
· Often not required for underground storage tank
(UST) remediation projects
· Typically performed as a revision of the
community relations plan
Permitting
Obtain permits or comply
· Provide for installing new monitoring wells
with substantive require· Provide for management of investigation-derived
ments, as applicable
waste (IDW)
· Projects conducted under CERCLA are not
required to obtain permits, but must meet
substantive permitting requirements
Reporting
Provide adequate documen- · Provide written monthly reports
tation of project activities,
· Perform site trips and provide verbal progress
status, problems, and
updates, as required
corrective actions
· Document significant decisions with written
telephone record
· Provide meeting agenda and minutes
(a) Only required under CERCLA or RCRA CA regulatory framework.
Typical Performance
Time
1 to 3 months
· 1 to 3 months
· Prepared in parallel
with project
management plan
· As needed, usually
prior to the detailed
site characterization
· 1 to 4 months
Continues throughout
the project
q A delineation of the authority and responsibility of
the QA/QC function
q Make a preliminary determination of the
feasibility of air sparging for the site
q A description of the organization’s total concept,
requirements, and scope of effort for achieving
and verifying quality.
q Develop a work plan for the detailed site
characterization and assessment.
I.3.2
I.3.3
Preliminary Assessment of
Air Sparging
Detailed Site Evaluation and
Feasibility Analysis
The purpose at this stage is to collect site data and
document site conditions to allow definitive assessment
of the feasibility of air sparging, document the basis for
recommending air sparging, build a consensus with regulators and the public for using air sparging, and document the acceptance of air sparging at the site. The
major tasks included in the detailed site evaluation are
summarized in Table I-3. The SOW requires the contractor to provide the labor, equipment, materials, and
facilities to accomplish the following objectives:
The purpose of the preliminary assessment is to
allow the contractor to establish an understanding of the
conditions and challenges at the site based on existing
data and reports, to evaluate the feasibility of air sparging, and to prepare a plan for the detailed assessment, if
needed. The major tasks included in the preliminary
assessment are summarized in Table I-2. The SOW
requires the contractor to provide the labor, equipment,
materials, and facilities to accomplish the following
objectives:
q Develop all required assessment information to
demonstrate that air sparging is an applicable
q Review available data, develop a conceptual
model, and assess site conditions
I-6
TABLE I-2. Statement of Work Requirements for Air Sparging: Preliminary Assessment in
Support of Air Sparging
Task Name
Review regulatory
acceptance of air
sparging
Task Scope
Determine if existing
regulations in the applicable
jurisdiction allow air sparging
as a remedial alternative
Collect and organize Review and organize existing
existing data
data into a usable format
Develop a preliminary conceptual site
model to assess
applicability of air
sparging based on
risk factors
Use existing data to develop
an understanding of site
location, history, description,
climate, demography, and land
use
Task Guidance and Information
The contractor should demonstrate specific
experience with regulatory status of air sparging
under the applicable jurisdiction and regulatory
framework
· Organize data into a comprehensive database
consistent with the Geographic Information
System (GIS) or other format specified by the
Navy
· Perform QA review to validate data for
completeness and accuracy
· Specify acceptable electronic data formats in
SOW to ensure compatibility
Develop map(s) showing major site features such
as property boundaries, land use, populations,
ecological features, and groundwater uses
Use existing data to develop
an understanding of the COCs
and nature and extent of
contamination
Assess applicability
of air sparging to
achieve remedial
objectives based on
the site-specific
characteristics
Typical
Performance
Time
1 to 2 months
1 to 3 months
1 to 4 months
Review/develop maps and figures defining the
location of sources and the distribution of contaminants in the environment above regulatory limits
and conservative risk-based screening
concentrations
Use existing site geology and · Document current status of information about
hydrology data to develop an
site geology and hydrology
understanding of groundwater · Define groundwater flow regimes, including
flow regimes
principal aquifers and direction and rate of
groundwater flow
Use existing data to identify
· Develop a basic understanding of contaminant
potential exposure pathways
behavior in the environment and identify
and assess the presence of
potential migration pathways, exposure points,
immediate or imminent threats
exposure routes, and receptors
that could preclude air
· Identify potential compliance points
sparging
Determine if the presence of
· Identify technical constraints that eliminate air
free product or other site
sparging as an alternative
factors constrain the ability to · Consider supplemental technologies to mitigate
implement air sparging
constraints
· Ensure that releases have been adequately
assessed and that sources are understood and
controlled
Establish a conceptual model Assess immediate and/or imminent effects of
with sufficient detail to allow a contaminants on potential human and
preliminary assessment of the environmental receptors
applicability of air sparging
· Use site data to determine if Air sparging does offer many advantages over
· 1 to 2
air sparging is applicable at competing remediation technologies, but is not
months
applicable in all situations. See Guidance
site
· Performed in
Document for details on advantages and
· Determine the extent of
parallel with
limitations of air sparging.
additional characterization
conceptual
required
model
development
I-7
TABLE I-2. Statement of Work Requirements for Air Sparging: Preliminary Assessment in
Support of Air Sparging (continued)
Task Name
Prepare preliminary
assessment report
and work plan and
submit to regulatory
agencies
Prepare preliminary
data collection
Quality Assurance
Project Plan (QAPP)
Task Scope
Prepare a report describing the
conceptual model, preliminary
evaluation, and plans for
collecting data required for
detailed evaluation; incorporate regulatory input
Prepare a plan to control the
quality of preliminary data
collection
Task Guidance and Information
· Document site status
· Define technical basis supporting applicability of
air sparging
· Document extent of additional characterization
if any is required
· Define QA/QC organization, responsibilities,
and authorities
· Specify definable features of work and quality
measures
· Describe field QA/QC
· Describe sampling and analytical QA/QC
· Describe equipment maintenance QA/QC
· Describe change control methods
· Describe corrective action methods
Prepare preliminary Prepare a plan to maintain
Compliance with OSHA requirements; specifically
data collection HASP safe working conditions during 29 CFR 1910.120, 29 CFR 1910.1200, and 29
preliminary data collection
CFR 1926
Support public
meetings
Prepare materials and attend
public meetings
· Prepare presentation materials, technical
summaries, and handouts
· Attend public meetings to support Naval
personnel
· Allow for two-way communication and response
to community concerns in project plans
Typical
Performance
Time
1 to 4 months
· 1 to 2
months
· Performed in
parallel with
work plan
preparation
· 1 to
2 months
· Performed in
parallel with
work plan
preparation
As required
TABLE I-3. Statement of Work Requirements for Air Sparging: Detailed Site Evaluation
and Feasibility Analysis
Task Name
Install required wells
and monitoring points
Task Scope
Install wells as
needed to ensure
samples can be
collected to evaluate
status of air sparging
Establish applicability Demonstrate that site
of air sparging through conditions should
site characterization
allow volatilization/biodegradation
of COCs upon
implementation of an
air sparging system
Task Guidance and Information
· Obtain applicable permits
· Comply with applicable rules and regulations
· Wells in plume at compliance point required
· Collect primary data (geochemical parameters and
contaminant concentrations) throughout the plume and
along flowpath transects
· Construct contour maps for each primary COC
· Evaluate data for evidence to support or rule out air
sparging as an applicable remedial alternative
· Identify needs for optional studies to support air
sparging
I-8
Typical
Performance
Time
1 to 2 months
Performed in
parallel with
evaluating
plume status
TABLE I-3. Statement of Work Requirements for Air Sparging: Detailed Site Evaluation
and Feasibility Analysis (continued)
Task Name
Task Scope
Evaluate plume status Characterize plume
chemistry and geochemistry to evaluate
applicability of air
sparging and for
optimizing
implementation
Perform fate and
Perform modeling to
transport modeling as predict the timeneeded to demondependent behavior of
strate protection of
contaminant concenhuman health and the trations with and
environment and
without
determine the time
biodegradation
required to achieve
site-specific
remediation goals
Compare air sparging Conduct a technology
to other remediation
screening to ensure
alternatives
that air sparging offers
the best balance of
effectiveness, implementability, and cost
Prepare air sparging
Prepare a report
evaluation report and describing the evalusubmit to regulatory
ation of air sparging,
agencies (and public if recommending (or
applicable)
rejecting) air sparging
as an effective remedial alternative, and
incorporating regulatory and public input
Support public
meetings
Task Guidance and Information
· Use historical data and collect additional site
characterization data as necessary to evaluate and
optimize implementation of remedial system
· Evaluate significant trends
· Construct contaminant contour maps
· Establish if there has been a loss of contaminant mass
over time
· Refine site-specific conceptual model
· Select model and define inputs
· Construct and calibrate model to site conditions
· Perform predictive simulations to estimate
concentrations at compliance points and time to reach
remediation goals
· Identify a comprehensive listing of candidate
technologies
· Perform technology screening using criteria required
by regulations
Typical
Performance
Time
1 to 2 months
Performed in
parallel with
evaluation of
plume status
1 to 2 months
· Document evidence supporting decision to implement 1 to 4 months
(or not implement) air sparging at the site
· Document information and technical analysis used to
demonstrate that air sparging will protect human
health and the environment
· Document information and technical analysis used to
determine time to reach remediation goals
· Provide technical basis for setting compliance points
and action levels to ensure protection of human health
and the environment
· Provide technical basis for setting remediation goals
for air sparging closeout
· Project future trends to be used to evaluate
performance during performance monitoring
· Quantify uncertainties in predictions
· Recommend air sparging, if appropriate, and obtain
regulatory and public consensus
· Document results of alternative screening
Prepare materials and · Prepare presentation materials, technical summaries, As required
attend public
and handouts
meetings
· Attend public meetings to support Naval personnel
· Allow for two-way communication and response to
community concerns in project plans
I-9
area, conducting a pilot-scale test, and preparing design
drawings and documentation for the full-scale installation. Once the proposed full-scale system is approved
by all involved parties, the system is constructed as
designed. The major tasks included in the system design
are summarized in Table I-4. The SOW requires the
contractor to provide the labor, equipment, materials,
and facilities to accomplish the following aspects of air
sparging system design and construction:
remediation technology based on field data and
previous use of air sparging at sites with similar
types of contamination
q Develop all required assessment information to
demonstrate that air sparging will adequately protect human health and the environment at the site
q Refine the conceptual site model
q Demonstrate that cleanup objectives for the site
can be achieved within a reasonable time frame
using air sparging
q Target treatment area identification
q Pilot-scale testing
q Establish and document a consensus among the
technical and regulatory community and the public
that air sparging will adequately protect human
health and the environment at the site.
q Air injection system design and installation
I.3.4
q Develop a Performance Monitoring Plan,
including a Contingency Plan (and obtain
regulatory acceptance)
q Soil vapor extraction system design and
installation
System Design and Installation
The purpose at this stage is to design the air sparging
system to achieve the established remediation goals
based on the site-specific characteristics and assessments performed in the previous steps. Air sparging system design consists of identifying the target treatment
TABLE I-4.
q Monitoring well placement and construction
q Monitoring point placement and construction.
Statement of Work Requirements for Air Sparging: System Design
Task Name
Prepare HASP
Task Scope
Prepare a plan to
maintain safe working
conditions during system
construction
Determine
Determine in which area
Target
the air sparging system
Treatment Area will be installed
Pilot Scale
Testing
Perform pilot scale
testing in portion of
target treatment area
Air
Injection
System
Design and install air
injection system
Task Guidance and Information
Ensure compliance with OSHA requirements; specifically 29
CFR 1910.120, 29 CFR 1910.1200, and 29 CFR 1926
Typical
Performance
Time
1 month
· Based on site characterization and regulatory requirements 1 month
· This may include the source zone, localized areas having
elevated concentrations within the plume, or the entire
plume area
1 to 3 months
· May be necessary to conduct the test in more than one
location if the site is large and soils types vary significantly
through the site
· Look for indicators of infeasibility
· Characterize the air distribution and baseline parameters
· Identify safety hazards to be addressed in full-scale design
1 to 3 months
· Determine injection well placement
· Determine injection well design
· Typically vertical wells are installed either direct-push
techniques or traditional auger drilling, horizontal wells may
also be necessary depending on the site conditions (rare)
· Determine the air injection flowrate and pulse frequency
· Identify compressors or blowers for air supply
I-10
TABLE I-4.
Statement of Work Requirements for Air Sparging: System Design
Task Name
Soil Vapor
Extraction
System
Prepare
Performance
Monitoring Plan
and submit to
regulatory
agencies
Prepare
monitoring
QA/QC
Program Plan
Design and
Install
Monitoring
Wells
Design and
Install
Monitoring
Points
Provide
construction
quality
assurance
I.3.5
Typical
Performance
Time
1 to 3 months
Task Scope
Design and install soil
vapor extraction system
Task Guidance and Information
· In general, air sparging systems that do not require SVE
are preferred
· Guidance documents are available for SVE installation
Develop a plan, cost
2 to 5 months
· Define scope and objectives of performance monitoring
estimate, and schedule · Arrange wells to make maximum use of existing facilities
for performance
and equipment
monitoring and
· Establish analytical requirements
evaluation to implement · Establish sampling frequency and duration
air sparging at the site
· Specify location of compliance points and protective action
and obtain regulatory
limits
acceptance
· Describe data reduction and evaluation of air sparging
progress
· Specify data format consistent with GIS requirements
· Plan for actions if air sparging progress or operation
deviates from expectations (Contingency Plan)
· Provide quantitative definition of remediation goals
· Identify institutional controls that are required during
performance monitoring
· Develop project schedule and definitive cost estimate
(+15% to -5%)
Prepare a plan to control · Define QA/QC organization, responsibilities, and authorities · 1 to 3
the quality of
months
· Specify definable features of work and quality measures
performance monitoring · Describe field QA/QC
· Performed in
parallel with
· Describe sampling and analytical QA/QC
preparing the
· Describe equipment maintenance QA/QC
Performance
· Describe change control methods
Monitoring
· Describe corrective action methods
Plan
Install wells as needed
1 to 2 months
· Monitoring wells are traditional wells with larger screened
to ensure samples can
intervals
be collected to evaluate · Comply with applicable rules and regulations
progress of air sparging
toward remediation
goals
Install monitoring points · Monitoring points are smaller than traditional wells and
1 to 2 months
as needed to ensure
designed to collect discrete samples
sampling is adequate to · Comply with applicable rules and regulations
evaluate progress of air
sparging toward
remediation goals
Provide on-site
Daily during
· Perform daily inspections
inspection and
construction
· Identify and correct deficiencies
documentation to ensure · Document results
compliance with quality
requirements
System Operation and Optimization
remedial goals. Operation, optimization, and monitoring
efforts must be focused on these specific remedial project objectives. Generally and typically, these include
maximum mass removal efficiency with respect to both
time and money, minimizing O&M costs, and achieving
This portion of the project involves operating, maintaining, and monitoring the remediation system throughout the period of operation needed to meet the established
I-11
site closure. The major tasks included in system operation and optimization are summarized in Table I-5. The
SOW requires the contractor to provide the labor, equipment, materials, and facilities to accomplish the following objectives:
performance of air sparging; make recommendations
concerning future remedial and monitoring activities,
and finally, when site-specific remediation goals have
been achieved, document the completion of remediation
activities. The major tasks included under performance
monitoring and site closure are summarized in Table I-6.
The SOW requires the contractor to provide the labor,
equipment, materials, and facilities to accomplish the
following objectives:
q Install any required facilities (e.g., monitoring
wells)
q System startup
q Execution of Performance Monitoring Plan,
previously established
q Optimize system operation based on initial
monitoring of system performance
q Install any required facilities (e.g., additional
monitoring wells or monitoring points)
q Establish/implement institutional controls (if
needed).
I.3.6
q Establish/implement institutional controls (if
needed)
Long-Term Monitoring and Site Closure
q Periodically collect performance monitoring data
until remedial action goals are achieved
The purpose of this stage is to collect site data and
perform technical analyses to quantitatively evaluate the
TABLE I-5. Statement of Work Requirements for Air Sparging: System Operation
and Optimization
Task Name
Prepare HASP
Task Scope
Task Guidance and Information
Prepare a plan to maintain safe Ensure compliance with OSHA requirements;
working conditions during
specifically 29 CFR 1910.120, 29 CFR
system operation and
1910.1200, and 29 CFR 1926
monitoring
Install required
wells and
monitoring points
System startup
Install additional wells as
needed to ensure samples can
be collected to evaluate
progress of air sparging and to
optimize system efficiency
Perform system startup
System
optimization/
operation
Optimize the operation of
system based on initial
monitoring data
Establish
institutional
controls as
required
Provide institutional controls to
protect human health and the
environment during system
operation and monitoring, if
needed
Comply with applicable rules and regulations
Start up procedures include checking all
components of the system to ensure the
system is ready for operation and running
properly as well as determining baseline
preremediation conditions at the site
· Adjust operating parameters, install
additional wells as necessary to improve
system efficiency
· Look for opportunity to transition to natural
attenuation when contaminant mass that can
cost-effectively be removed is removed
Place access restrictions, deed restrictions,
easement, and other controls as needed during
operation and monitoring period
I-12
Typical
Performance Time
· 1 month
· Performed in
parallel with
preparing the
Performance
Monitoring Plan
1 to 2 months
1 week
· 6 to 24 months
· Performed
throughout the
duration of the
operation period
· 1 to 2 months
· Performed in
parallel with well
installation
TABLE I-6. Statement of Work Requirements for Air Sparging: Long-Term Monitoring and Site
Closure
Task Name
Conduct
performance
monitoring
Task Scope
Task Guidance and Information
Collect and analyze
· Collect samples in and around the plume and at
samples to support
compliance points until remedial action goals are
evaluation of the
achieved
progress of air sparging · Comply with Performance Monitoring Plan, QA/QC
Program Plan, and HASP
Install required
Install additional wells
Comply with applicable rules and regulations
wells and
as needed to ensure
monitoring points samples can be
collected to evaluate
progress of air sparging
Evaluate progress Determine if air sparging · Compare plume status to site-specific remediation
of air sparging
is proceeding as
goals and expected progress and recommend
expected and recomcontinued monitoring (expected progress), corrective
mend corrective action
action (significant unexpected results), or closeout
for unexpected results
(remediation goals achieved)
· Update conceptual model and revise model
predictions
· Update remediation time predictions
Prepare perform- Report results and
Document methods, results, and QA activities for
ance monitoring
obtain regulatory
monitoring period
and performance approval
assessment
reports
Prepare closure
report
Prepare a report documenting remediation
activities and results and
formal acceptance of
site closure or transition
to monitored natural
attenuation
Establish institu- Establish any required
tional or adminiinstitutional or
strative controls
administrative controls
Restore and close Perform well abandonsite
ment as required
Typical
Performance Time
1 to 5 years (rare)
1 to 2 months
Performed in
parallel with
performance
monitoring
· 1 to 2 months
preparation time
· Performed
periodically as
defined in
Performance
Monitoring Plan
2 to 5 months
· Demonstrate protection of human health and the
environment
· Quantify, on a statistical basis, the attainment of sitespecific remediation goals and level of confidence
· Demonstrate removal of contaminant mass that can
cost-effectively be removed and evidence to support
transitioning to natural attenuation or site closure
Place any required physical access controls and legal
2 to 5 months
restrictions to ensure land use is consistent with risk
scenarios
2 to 5 months
· Conform with local regulatory requirements for
closing unneeded wells
· Ensure that any wells left in place cannot be used for
purposes other than intended
· Abandon unneeded wells using methods that prevent
migration of contaminants into an aquifer or between
aquifers and reduce the potential for vertical or
horizontal migration of fluids in or around the well
· Secure remaining wells to prevent unauthorized
access
q Periodically evaluate the progress of air sparging
with respect to predicted behavior
remedial action (i.e., implementation of monitored
natural attenuation) or site closure, as appropriate
q Make recommendations for continued monitoring,
reassessment of the conceptual model, alternative
q Document all monitoring activities and site data
collected throughout operational period
I-13
q Report progress of remedial effort to regulators, as
appropriate
The work elements required to perform air sparging
frequently involve the use of existing sampling wells and
monitoring points. The SOW must provide a description
of the number, location, and construction of wells and
monitoring points in and around the area to be
remediated.
The SOW must clearly define responsibilities for
managing investigation-derived wastes (IDW). Facility
limitations and existing waste management facilities
located at the site, which are appropriate for managing
any IDW, must be described.
q Document compliance with remedial goals
q Establish institutional controls (if needed)
q Complete site closure activities, including a site
closure report.
I.4
Government-Furnished Property
The SOW must specify that the contractor is expected
to be self-sufficient for all work to be performed (except
possibly utilities [power, phone, sewer, etc.]), unless specific site conditions require use of government-furnished
property.
I.5
I.6
A list of the deliverable items to be produced during
the project, with a clear indication of the due date for
each item, appears in the SOW. Table I-7 is provided as
an example to assist in preparation of the deliverables
list. The number of days to complete each deliverable is
project-specific and should be defined as the SOW is
prepared. The number of copies, print and electronic
format, and addresses of recipients should be defined in
the SOW.
Government-Furnished Facilities
Facility personnel must provide the implementing
contractor access to the site to be remediated. The SOW
must define the requirements for contractor personnel to
enter the facility and work at the site.
TABLE I-7.
Deliverables
Example Deliverables for an Air Sparging Project
Deliverable
Draft program management plan(b)
Number of
Due Date(a)
Copies
5
[Number] days after project start
Applicable Task
Planning and
management
Final program management plan(b)
10
Draft community relations plan(b)
Final community relations plan(b)
5
10
Input for permit applications (e.g.,
well construction permits)
Monthly reports
Meeting agendas
Telephone records, trip reports, and
meeting minutes
Draft assessment report and work
plan for detailed evaluation(c)
Final assessment report and work
plan for detailed evaluation(c)
Public meeting support
Draft detailed evaluation report
Preliminary
assessment
5
[Number] days after receiving comments on
the draft plan
[Number] days after project start
[Number] days after receiving comments on
the draft plan
As required
1
15
1
[Number] days after the first of each month
[Number] days before the event
[Number] days after the event
5
10
Detailed assessment
—
5
Final detailed evaluation report
10
Public meeting support
—
I-14
[Number] days after approval of project
management plan
[Number] days after receiving comments on
the draft work plan
As required
[Number] days after approval of the final work
plan
[Number] days after receiving comments on
the draft report
As required
TABLE I-7.
Example Deliverables for an Air Sparging Project (continued)
Deliverable
Applicable Task
Draft Performance Monitoring Plan(c) Performance
monitoring
Final Performance Monitoring Plan(c)
Draft System Design Plans
System design and
installation
Final System Design Plans
System Installation
Construction QA Reports
Draft As-Built Drawings
Performance
monitoring
System design
Number of
Copies
Due Date(a)
5
[Number] days after approval of the final site
technology evaluation report
10
[Number] days after receiving comments on
the draft plan
5
[Number] days after approval of the final site
technology evaluation report
10
[Number] days after receiving comments on
the draft plan
—
As required
1
Daily during field activities
5
Final As-Built Drawings
Performance Monitoring/
Performance Assessment Reports
Draft Site Closure Report
10
Performance
monitoring
Project closeout
5
5
Final Site Closure Report
10
[Number] days after approval of the final site
technology evaluation report
[Number] days after receiving comments on
the draft plan
Periodically as required in the Performance
Monitoring Plan
[Number] days after approval of the final
Performance Monitoring Plan
[Number] days after receiving comments on
the draft report
(a) Tables in Section I.3 indicate typical task durations.
(b) These deliverables are only required under CERCLA or RCRA CA regulatory frameworks.
(c) Includes site-specific QA/QC Program Plan and HASP.
I.7
Tri-Service/U.S. Environmental Protection Agency Working
Group. 1998. Environmental Site Closeout Process. Working draft.
References
Battelle. 1999. User’s Manual for Implementing Remediation
by Natural Attenuation at Petroleum Release Sites. Prepared for the Naval Facility Engineering Command (Various Divisions). May.
U.S. Environmental Protection Agency. 1995. Remedial
Design/Remedial Action Handbook. EPA/540/R-95/059.
Office of Emergency and Remedial Response,
Washington, DC.
Leeson, A., P.C. Johnson, R.L. Johnson, R.E. Hinchee, and
D.B. McWhorter. 2001. Air Sparging Design Paradigm.
In press. December 31.
U.S. EPA, see U.S. Environmental Protection Agency.
I-15